$(function(){})的执行过程分析

作者:zccst

首先,$(function(){})是$(document).ready(function(){})的简写形式。

 

在日常使用中,我们会把代码写到$(function(){})中,今天看看jQuery是如何做的(过程有点长)。

 

1,看jQuery入口,结论是$(function(){})是$(document).ready(function(){})的简写形式

$(function(){})相对于$()中传入了一个function类型的数据。根据源码:

jQuery.fn = jQuery.prototype = {

    init:function( selector, context, rootjQuery ) {

        if ( jQuery.isFunction( selector ) ) {
            return rootjQuery.ready( selector );
        }

    }

}

而rootjQuery就是$(document),见866行源码

// All jQuery objects should point back to these
rootjQuery = jQuery(document);

 

2,$(document).ready(function(){})是如何实现的呢?

从$().ready()的调用方式可以看出,ready是对象方法,见240行源码

ready: function( fn ) {
    // Add the callback
    jQuery.ready.promise().done( fn );

    return this;
},

可以看出,jQuery.ready.promise()是一个对象,调用了done(fn)方法,表明调用了一个延迟对象,再看一下jQuery.ready.promise()

 1 jQuery.ready.promise = function( obj ) {
 2     if ( !readyList ) {
 3 
 4         readyList = jQuery.Deferred();
 5 
 6         // Catch cases where $(document).ready() is called after the browser event has already occurred.
 7         // we once tried to use readyState "interactive" here, but it caused issues like the one
 8         // discovered by ChrisS here: http://bugs.jquery.com/ticket/12282#comment:15
 9         if ( document.readyState === "complete" ) {
10             // Handle it asynchronously to allow scripts the opportunity to delay ready
11             setTimeout( jQuery.ready );//调用工具方法jQuery.ready
12 
13         } else {
14 
15             // Use the handy event callback
16             document.addEventListener( "DOMContentLoaded", completed, false );
17 
18             // A fallback to window.onload, that will always work
19             window.addEventListener( "load", completed, false );//回调函数在90行,也调用工具方法jQuery.ready
20         }
21     }
22     return readyList.promise( obj );
23 };

 

posted @ 2014-05-24 12:51  走走停停走走  Views(995)  Comments(0Edit  收藏  举报