点击页面判断是否安装app并打开，否则跳转app store的方法

常常有这样的场景，咱们开发出来的APP需要进行推广，比如在页面顶部来一张大Banner图片，亦或一张二维码。但往往我们都是直接给推广图片加了一个下载链接（App Store中的）。所以咱们来模拟一下用户的操作步骤： 

1、用户第一次访问宣传页面 

a、点击Banner，进入到APP Store中对应的APP下载页 

b、APP下载页中提示：安装；用户点击安装 

c、安装完成后，APP下载页中提示：打开；用户继续点击打开 

d、用户正常使用APP 

2、用户第二次访问宣传页面 

a、点击Banner，进入到APP Store中对应的APP下载页 

b、APP下载页中提示：打开；用户直接点击打开 

c、用户正常使用APP 

3、用户第三次、第四次、…、第N次访问，操作步骤同2 

能看出来，不管是点击Banner还是扫描二维码的方式，对于已经安装过APP的用户来说，这个体验都是非常糟糕的。 

更优的体验是：点击Banner（或扫描二维码）后，程序判断当前系统是否已安装App，如果未安装，则自动跳转到App Store下载页；否则直接打开App。 

在iOS上，要增加一个APP的大Banner，其实只需要在标签内增加一个标签即可，格式如：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">meta</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">'apple-itunes-app'</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">content</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">'app-id=你的APP-ID'</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

比如加一个百度贴吧的Native APP大Banner，用下面这串儿代码：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">meta</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">name</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">'apple-itunes-app'</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">content</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">'app-id=477927812'</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

而对于点击链接后，能否直接打开，可以通过下面的代码来实现。前提条件：你得知道你的APP对应的打开协议，如贴吧APP，协议为：com.baidu.tieba:// ，微信的：weixin:// ，and so on。。。 

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"text/javascript"</span>></span><span class="javascript" style="box-sizing: border-box;">
document.getElementById(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'openApp'</span>).onclick = <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(e)</span>{</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 通过iframe的方式试图打开APP，如果能正常打开，会直接切换到APP，并自动阻止a标签的默认行为</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 否则打开a标签的href链接</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> ifr = document.createElement(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'iframe'</span>);
ifr.src = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.baidu.tieba://'</span>;
ifr.style.display = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'none'</span>;
document.body.appendChild(ifr);
window.setTimeout(<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>
document.body.removeChild(ifr);
},<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3000</span>)
};
</span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

当然，如果你是设计成一张二维码，可以用下面这段代码： 

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"text/javascript"</span>></span><span class="javascript" style="box-sizing: border-box;">
document.getElementById(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'openApp'</span>).onclick = <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">(e)</span>{</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 通过iframe的方式试图打开APP，如果能正常打开，会直接切换到APP，并自动阻止a标签的默认行为</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 否则打开a标签的href链接</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">var</span> ifr = document.createElement(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'iframe'</span>);
ifr.src = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.baidu.tieba://'</span>;
ifr.style.display = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'none'</span>;
document.body.appendChild(ifr);
window.setTimeout(<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">function</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span>{</span>
document.body.removeChild(ifr);
},<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3000</span>)
};
document.getElementById(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'openApp'</span>).click();</span></code>