JS 脚本应该放在页面哪个位置 head body foot

2017-01-12 19:03:38来源:cnblogs.com作者:碎碎虎人点击

我们平时在页面上写JS 是放在头部<head>中呢 还是放到body 最下面 能更优化?

查了一番资料,推荐 放在页面底部如:

<html>    <head>        <title>My awesome page</title>        <!-- CSS -->        <link rel="stylesheet" type="text/css" href="...">        <link rel="stylesheet" type="text/css" href="...">        <link rel="stylesheet" type="text/css" href="...">        <link rel="stylesheet" type="text/css" href="...">    </head>    <body>        <!-- Content content content -->        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>        <script type="text/javascript" src="..."></script>        <script type="text/javascript" src="..."></script>        <script type="text/javascript" src="..."></script>    </body></html>

WHY?

The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames. More...

CSS

A little bit off-topic, but... Put stylesheets at the top.

While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively. More...

参考:

http://stackoverflow.com/questions/196702/where-to-place-javascript-in-a-html-file

https://developer.yahoo.com/performance/rules.html#js_bottom=

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