jquery.ready可以在文档加载后尽快执行对文档的操作

 1 jQuery.ready.promise = function( obj ) {
 2     if ( !readyList ) {
 3 
 4         readyList = jQuery.Deferred();
 5 
 6         // Catch cases where $(document).ready() is called
 7         // after the browser event has already occurred.
 8         // Support: IE6-10
 9         // Older IE sometimes signals "interactive" too soon
10         if ( document.readyState === "complete" ||
11             ( document.readyState !== "loading" && !document.documentElement.doScroll ) ) {
12 
13             // Handle it asynchronously to allow scripts the opportunity to delay ready
14             window.setTimeout( jQuery.ready );
15 
16         // Standards-based browsers support DOMContentLoaded
17         } else if ( document.addEventListener ) {
18 
19             // Use the handy event callback
20             document.addEventListener( "DOMContentLoaded", completed );
21 
22             // A fallback to window.onload, that will always work
23             window.addEventListener( "load", completed );
24 
25         // If IE event model is used
26         } else {
27 
28             // Ensure firing before onload, maybe late but safe also for iframes
29             document.attachEvent( "onreadystatechange", completed );
30 
31             // A fallback to window.onload, that will always work
32             window.attachEvent( "onload", completed );
33 
34             // If IE and not a frame
35             // continually check to see if the document is ready
36             var top = false;
37 
38             try {
39                 top = window.frameElement == null && document.documentElement;
40             } catch ( e ) {}
41 
42             if ( top && top.doScroll ) {
43                 ( function doScrollCheck() {
44                     if ( !jQuery.isReady ) {
45 
46                         try {
47 
48                             // Use the trick by Diego Perini
49                             // http://javascript.nwbox.com/IEContentLoaded/
50                             top.doScroll( "left" );
51                         } catch ( e ) {
52                             return window.setTimeout( doScrollCheck, 50 );
53                         }
54 
55                         // detach all dom ready events
56                         detach();
57 
58                         // and execute any waiting functions
59                         jQuery.ready();
60                     }
61                 } )();
62             }
63         }
64     }
65     return readyList.promise( obj );
66 };