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jquery源码阅读之jquery.extend

2015-08-08 15:57 561 查看

jquery.extend 在众多插件中都有应用，最常见的应用是把插件默认的参数和用户输入的参数进行合并，用户没有输入的参数则用插件默认的参数，设置了，则采用用户设置的参数;

首先我们看看jquery.extend API的解释：这里

测试代码：

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery.extend demo</title>
<script src="../jquery-1.7.1.js"></script>
<script src="../bobojq.js"></script></head>
<body>

<div id="log"></div>

<script>
var object1 = {
apple: 0,
banana: { weight: 52, price: 100 },
cherry: 97
};
var object2 = {
banana: { price: 200 },
durian: 100
};
var o = {};
o.n1 = o;
$.extend(true,o,{n2:o}); //测试无线循环
//$.extend( object1, object2 );//非深度
$.extend( true, object1, object2 );//深度
// Assuming JSON.stringify - not available in IE<8
$( "#log" ).append( JSON.stringify( object1 ) );
</script>

</body>
</html>

jquery.extend 源码阅读：

jQuery.extend = jQuery.fn.extend = function() {
var src, copyIsArray, copy, name, options, clone,
target = arguments[0] || {},
i = 1,
length = arguments.length,
deep = false;

// Handle a deep copy situation 如过第一个参数是布尔值则调整修正参数顺序 例如$.extend( true, object1, object2 );
if ( typeof target === "boolean" ) {
deep = target;
target = arguments[1] || {};
// skip the boolean and the target
i = 2;
}

// Handle case when target is a string or something (possible in deep copy) //对于目标对象非对象和函数的，例如字符串修成为对象
if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
target = {};
}

// extend jQuery itself if only one argument is passed //如果只有一个对象参数则认和jquery合并
if ( length === i ) {
target = this;
--i;
}

for ( ; i < length; i++ ) {
// Only deal with non-null/undefined values
if ( (options = arguments[ i ]) != null ) {
// Extend the base object
for ( name in options ) {
src = target[ name ];
copy = options[ name ];

// Prevent never-ending loop 防止进入无线循环
if ( target === copy ) {
continue;
}

// Recurse if we're merging plain objects or arrays 深度和非深度的区别
/*
var object1 = {apple: 0,banana: { weight: 52, price: 100 },cherry: 97};
var object2 = {banana: { price: 200 },durian: 100};
$.extend(object1,object2) {"apple":0,"banana":{"price":200},"cherry":97,"durian":100}
$.extend(true,object1,object2) {"apple":0,"banana":{"weight":52,"price":200},"cherry":97,"durian":100}
*/
if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
if ( copyIsArray ) {
copyIsArray = false;
clone = src && jQuery.isArray(src) ? src : [];

} else {
clone = src && jQuery.isPlainObject(src) ? src : {};
}

// Never move original objects, clone them
target[ name ] = jQuery.extend( deep, clone, copy );

// Don't bring in undefined values
} else if ( copy !== undefined ) { // 一般常用的是这个
target[ name ] = copy;
}
}
}
}

// Return the modified object
return target;
};

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