异步.js文件加载语法 [英] asynchronous .js file loading syntax

问题描述

我注意到，有似乎是加载JS文件一对夫妇略有不同的语法异步，我想知道是否有任何两者之间的区别，或者如果他们都pretty非常重要的作用是相同的。我猜他们的工作是相同的，只是希望确保一种方法并不比其他更好的出于某种原因。 ：）

方法一

 （函数（）{
    变种D =文件，
    H = d.getElementsByTagName（头）[0]
    S = d.createElement（'脚本'）;
    s.type =文/ JavaScript的';
    s.src ='/ JS / myfile.js';
    h.appendChild（多个）;
}）（）; / *注后括号和大括号* /
 

结果
方法二（在Fa​​cebook的code看到这个）

 （函数（）{
    变种D =文件，
    H = d.getElementsByTagName（头）[0]
    S = d.createElement（'脚本'）;
    s.type =文/ JavaScript的';
    s.async = TRUE;
    s.src ='/ JS / myfile.js';
    h.appendChild（多个）;
}（））; / *注后括号和大括号* /
 

解决方案

这是我看到的唯一区别是 s.async = TRUE; 在Facebook的方法

  

的异步和延迟属性是表明脚本应该如何执行布尔属性。

  
  

有可以使用这些属性来选择三种可能的模式。 如果是present，那么脚本将被异步，只要它是可用执行异步属性。如果在异步属性不是present但defer属性为present，然后在页面完成解析执行脚本。如果没有属性是present，那么脚本被取出，并立即执行，用户代理继续解析页面之前。

来源和进一步阅读：<一href=\"http://www.whatwg.org/specs/web-apps/current-work/multipage/scripting-1.html#attr-script-async\">Whatwg.org HTML 5：脚本元素

至于优点，你可能要检查什么谷歌有这个去年12月说：

• 谷歌分析推出异步跟踪

I noticed that there seems to be a couple of slightly different syntaxes for loading js files asynchronously, and I was wondering if there's any difference between the two, or if they both pretty much function the same. I'm guessing they work the same, but just wanted to make sure one method isn't better than the other for some reason. :)

Method One

(function() {
    var d=document,
    h=d.getElementsByTagName('head')[0],
    s=d.createElement('script');
    s.type='text/javascript';
    s.src='/js/myfile.js';
    h.appendChild(s);
})(); /* note ending parenthesis and curly brace */

Method Two (Saw this in Facebook's code)

(function() {
    var d=document,
    h=d.getElementsByTagName('head')[0],
    s=d.createElement('script');
    s.type='text/javascript';
    s.async=true;
    s.src='/js/myfile.js';
    h.appendChild(s);
}()); /* note ending parenthesis and curly brace */

解决方案

The only difference that I notice is the s.async=true; in the Facebook method.

The async and defer attributes are boolean attributes that indicate how the script should be executed.

There are three possible modes that can be selected using these attributes. If the async attribute is present, then the script will be executed asynchronously, as soon as it is available. If the async attribute is not present but the defer attribute is present, then the script is executed when the page has finished parsing. If neither attribute is present, then the script is fetched and executed immediately, before the user agent continues parsing the page.

Source and Further reading: Whatwg.org HTML 5: The script element

As for the advantages, you may want to check what Google had to say on this last December:

• Google Analytics Launches Asynchronous Tracking

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