Jquery实现ready()的源码

 function bindReady(){
     if ( readyBound ) return;
     readyBound = true;     

     // Mozilla, Opera and webkit nightlies currently support this event
     if ( document.addEventListener ) {
         // Use the handy event callback
         document.addEventListener( "DOMContentLoaded", function(){
             document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
             jQuery.ready();
         }, false );     

     // If IE event model is used
     } else if ( document.attachEvent ) {
         // ensure firing before onload,
         // maybe late but safe also for iframes
         document.attachEvent("onreadystatechange", function(){
             if ( document.readyState === "complete" ) {
                 document.detachEvent( "onreadystatechange", arguments.callee );
                 jQuery.ready();
             }
         });     

         // If IE and not an iframe
         // continually check to see if the document is ready
         if ( document.documentElement.doScroll && typeof window.frameElement === "undefined" )
           (function(){
             if ( jQuery.isReady ) return;     

             try {
                 // If IE is used, use the trick by Diego Perini
                 // http://javascript.nwbox.com/IEContentLoaded/
                 document.documentElement.doScroll("left");
             } catch( error ) {
                 setTimeout( arguments.callee, 0 );
                 return;
             }     

             // and execute any waiting functions
             jQuery.ready();
         })();
     }     

     // A fallback to window.onload, that will always work
     jQuery.event.add( window, "load", jQuery.ready );
 }   

关键：IE or Webkit|Moz 内核判断、DOMContentLoaded事件、onreadystatechange事件、readyState==“complete”