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”