JavaScript继承详解（二）
2016-09-05 14:39
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版权声明：本文为博主原创文章，未经博主允许不得转载。
目录(?)[+]
这一章我们将会重点介绍JavaScript中几个重要的属性（this、constructor、prototype）， 这些属性对于我们理解如何实现JavaScript中的类和继承起着至关重要的作用。
先看一个在全局作用范围内使用this的例子：
函数中的this是在运行时决定的，而不是函数定义时，如下：
[javascript] view
plain copy
// 定义一个全局函数
function foo() {
console.log(this.fruit);
}
// 定义一个全局变量，等价于window.fruit = "apple";
var fruit = "apple";
// 此时函数foo中this指向window对象
// 这种调用方式和window.foo();是完全等价的
foo(); // "apple"
// 自定义一个对象，并将此对象的属性foo指向全局函数foo
var pack = {
fruit: "orange",
foo: foo
};
// 此时函数foo中this指向window.pack对象
pack.foo(); // "orange"
全局函数apply和call可以用来改变函数中this的指向，如下：
因为在JavaScript中函数也是对象，所以我们可以看到如下有趣的例子：
如果这个函数被用在创建自定义对象的场景中，我们称这个函数为构造函数。 比如下面一个简单的场景：
实际上，JavaScript所有的固有数据类型都具有只读的prototype属性（这是可以理解的：因为如果修改了这些类型的prototype属性，则哪些预定义的方法就消失了）， 但是我们可以向其中添加自己的扩展方法。
注意：这里有一个陷阱，向Array的原型中添加扩展方法后，当使用for-in循环数组时，这个扩展方法也会被循环出来。
下面的代码说明这一点（假设已经向Array的原型中扩展了min方法）：
但是当constructor遇到prototype时，有趣的事情就发生了。
我们知道每个函数都有一个默认的属性prototype，而这个prototype的constructor默认指向这个函数。如下例所示：
原来是因为覆盖Person.prototype时，等价于进行如下代码操作：
目录(?)[+]
这一章我们将会重点介绍JavaScript中几个重要的属性（this、constructor、prototype）， 这些属性对于我们理解如何实现JavaScript中的类和继承起着至关重要的作用。
this
this表示当前对象，如果在全局作用范围内使用this，则指代当前页面对象window； 如果在函数中使用this，则this指代什么是根据运行时此函数在什么对象上被调用。 我们还可以使用apply和call两个全局方法来改变函数中this的具体指向。先看一个在全局作用范围内使用this的例子：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 830px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"><script type=</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"text/javascript"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> === window); </span><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(window.alert === <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.alert); </span><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"&
1fff7
gt;.parseInt(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"021"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">, 10)); </span><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 10</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </script> </span></li></ol></div>函数中的this是在运行时决定的，而不是函数定义时，如下：
[javascript] view
plain copy
// 定义一个全局函数
function foo() {
console.log(this.fruit);
}
// 定义一个全局变量，等价于window.fruit = "apple";
var fruit = "apple";
// 此时函数foo中this指向window对象
// 这种调用方式和window.foo();是完全等价的
foo(); // "apple"
// 自定义一个对象，并将此对象的属性foo指向全局函数foo
var pack = {
fruit: "orange",
foo: foo
};
// 此时函数foo中this指向window.pack对象
pack.foo(); // "orange"
全局函数apply和call可以用来改变函数中this的指向，如下：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 1536px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 定义一个全局函数</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> foo() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.fruit); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 定义一个全局变量</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> fruit = </span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"apple"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 自定义一个对象</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> pack = { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> fruit: <span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"orange"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 等价于window.foo();</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo.apply(window); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// "apple"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 此时foo中的this === pack</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo.apply(pack); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// "orange"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>注：apply和call两个函数的作用相同，唯一的区别是两个函数的参数定义不同。因为在JavaScript中函数也是对象，所以我们可以看到如下有趣的例子：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 2105px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 定义一个全局函数</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> foo() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">if</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> === window) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"this is window."</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 函数foo也是对象，所以可以定义foo的属性boo为一个函数</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo.boo = <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">if</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> === foo) { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"this is foo."</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">else</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">if</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> === window) { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(<span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"this is window."</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 等价于window.foo();</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo(); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// this is window.</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 可以看到函数中this的指向调用函数的对象</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo.boo(); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// this is foo.</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 使用apply改变函数中this的指向</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> foo.boo.apply(window); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// this is window.</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>prototype
我们已经在第一章中使用prototype模拟类和继承的实现。 prototype本质上还是一个JavaScript对象。 并且每个函数都有一个默认的prototype属性。如果这个函数被用在创建自定义对象的场景中，我们称这个函数为构造函数。 比如下面一个简单的场景：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 2786px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 构造函数</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(name) { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name = name; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 定义Person的原型，原型中的属性可以被自定义对象引用</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype = { </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> getName: <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> zhang = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(zhang.getName()); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// "ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>作为类比，我们考虑下JavaScript中的数据类型 - 字符串（String）、数字（Number）、数组（Array）、对象（Object）、日期（Date）等。 我们有理由相信，在JavaScript内部这些类型都是作为构造函数来实现的，比如：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 3203px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 定义数组的构造函数，作为JavaScript的一种预定义类型</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Array() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// ...</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 初始化数组的实例</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr1 = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Array(1, 56, 34, 12); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 但是，我们更倾向于如下的语法定义：</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr2 = [1, 56, 34, 12]; </span></span></li></ol></div>同时对数组操作的很多方法（比如concat、join、push）应该也是在prototype属性中定义的。实际上，JavaScript所有的固有数据类型都具有只读的prototype属性（这是可以理解的：因为如果修改了这些类型的prototype属性，则哪些预定义的方法就消失了）， 但是我们可以向其中添加自己的扩展方法。
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 3592px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 向JavaScript固有类型Array扩展一个获取最小值的方法</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Array.prototype.min = <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> min = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">[0]; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">for</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> i = 1; i < </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.length; i++) { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">if</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">[i] < min) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> min = <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">[i]; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> min; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 在任意Array的实例上调用min方法</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log([1, 56, 34, 12].min()); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 1</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>注意：这里有一个陷阱，向Array的原型中添加扩展方法后，当使用for-in循环数组时，这个扩展方法也会被循环出来。
下面的代码说明这一点（假设已经向Array的原型中扩展了min方法）：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 4079px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr = [1, 56, 34, 12]; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> total = 0; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">for</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> i </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">in</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> total += parseInt(arr[i], 10); </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(total); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// NaN</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li></ol></div>解决方法也很简单：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 4340px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr = [1, 56, 34, 12]; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> total = 0; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">for</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (</span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> i </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">in</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">if</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> (arr.hasOwnProperty(i)) { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> total += parseInt(arr[i], 10); </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(total); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 103</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>constructor
constructor始终指向创建当前对象的构造函数。比如下面例子：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 4659px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 等价于 var foo = new Array(1, 56, 34, 12);</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> arr = [1, 56, 34, 12]; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(arr.constructor === Array); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 等价于 var foo = new Function();</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Foo = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { }; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(Foo.constructor === Function); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 由构造函数实例化一个obj对象</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> obj = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Foo(); </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(obj.constructor === Foo); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 将上面两段代码合起来，就得到下面的结论</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(obj.constructor.constructor === Function); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>但是当constructor遇到prototype时，有趣的事情就发生了。
我们知道每个函数都有一个默认的属性prototype，而这个prototype的constructor默认指向这个函数。如下例所示：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-bl
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height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(name) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name = name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype.getName = <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> p = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(Person.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// 将上两行代码合并就得到如下结果</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>当时当我们重新定义函数的prototype时（注意：和上例的区别，这里不是修改而是覆盖）， constructor的行为就有点奇怪了，如下示例：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 5519px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; posi
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border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(name) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name = name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype = { </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> getName: <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> p = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// false</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(Person.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// false</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// false</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>为什么呢？原来是因为覆盖Person.prototype时，等价于进行如下代码操作：
<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 5962px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">Person.prototype = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Object({ </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> getName: <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }); </span></li></ol></div>而constructor始终指向创建自身的构造函数，所以此时Person.prototype.constructor === Object，即是：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 6187px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(name) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name = name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype = { </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> getName: <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> p = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor === Object); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(Person.prototype.constructor === Object); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor.prototype.constructor === Object); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> </span></li></ol></div>怎么修正这种问题呢？方法也很简单，重新覆盖Person.prototype.constructor即可：<div class="dp-highlighter bg_javascript" style="font-family: Consolas, "Courier New", Courier, mono, serif; font-size: 12px; width: 700.906px; overflow-x: auto; overflow-y: hidden; padding-top: 1px; position: relative; margin: 18px 0px !important; background-color: rgb(231, 229, 220);"><div class="bar" style="padding-left: 45px;"><div class="tools" style="padding: 3px 8px 10px 10px; font-stretch: normal; font-size: 9px; line-height: normal; font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; color: silver; border-left: 3px solid rgb(108, 226, 108); background-color: rgb(248, 248, 248);"><strong>[javascript]</strong> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="ViewSource" title="view plain" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_plain.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">view plain</a><span data-mod="popu_168"> <a target=_blank href="http://blog.csdn.net/l1028386804/article/details/44133019#" class="CopyToClipboard" title="copy" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; text-indent: -2000px; background-image: url("images/default/ico_copy.gif"); background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;">copy</a></span><div style="position: absolute; left: 600px; top: 6556px; width: 18px; height: 18px; z-index: 99;"></div><span data-mod="popu_169"> </span><span class="tracking-ad" data-mod="popu_167"><a target=_blank href="https://code.csdn.net/snippets/614385" target="_blank" title="在CODE上查看代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/CODE_ico.png" width="12" height="12" alt="在CODE上查看代码片" style="border: none; max-width: 100%; position: relative; top: 1px; left: 2px;" /></a></span><span class="tracking-ad" data-mod="popu_170"><a target=_blank href="https://code.csdn.net/snippets/614385/fork" target="_blank" title="派生到我的代码片" style="color: rgb(160, 160, 160); text-decoration: none; border: none; padding: 1px; margin: 0px 10px 0px 0px; font-size: 9px; display: inline-block; width: 16px; height: 16px; background-image: none; background-attachment: initial; background-color: inherit; background-size: initial; background-origin: initial; background-clip: initial; background-position: left top; background-repeat: no-repeat;"><img src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="border: none; max-width: 100%; position: relative; top: 2px; left: 2px;" /></a></span></div></div><ol start="1" class="dp-c" style="padding: 0px; border: none; color: rgb(92, 92, 92); margin: 0px 0px 1px 45px !important; background-color: rgb(255, 255, 255);"><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(name) { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name = name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype = <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Object({ </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> getName: <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">function</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">() { </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">return</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">this</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">.name; </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> } </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> }); </span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> Person.prototype.constructor = Person; </span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> <span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">var</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> p = </span><span class="keyword" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 102, 153); font-weight: bold; background-color: inherit;">new</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> Person(</span><span class="string" style="margin: 0px; padding: 0px; border: none; color: blue; background-color: inherit;">"ZhangSan"</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;">); </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important; background-color: rgb(248, 248, 248);"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(Person.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li><li class="alt" style="border-top: none; border-right: none; border-bottom: none; border-left: 3px solid rgb(108, 226, 108); list-style: decimal-leading-zero outside; color: inherit; line-height: 18px; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="margin: 0px; padding: 0px; border: none; color: black; background-color: inherit;"> console.log(p.constructor.prototype.constructor === Person); <span class="comment" style="margin: 0px; padding: 0px; border: none; color: rgb(0, 130, 0); background-color: inherit;">// true</span><span style="margin: 0px; padding: 0px; border: none; background-color: inherit;"> </span></span></li></ol></div>
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