jQuery中的domReady分析

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

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

jQuery.ready.promise = function( obj ) {
    if ( !readyList ) {
　　　　　readyList = jQuery.Deferred();
        // Catch cases where $(document).ready() is called after the browser event has already occurred.
        // we once tried to use readyState "interactive" here, but it caused issues like the one
        // discovered by ChrisS here: http://bugs.jquery.com/ticket/12282#comment:15
        if ( document.readyState === "complete" ) {
            // Handle it asynchronously to allow scripts the opportunity to delay ready
            setTimeout( jQuery.ready );

        // Standards-based browsers support DOMContentLoaded
        } else if ( document.addEventListener ) {
            // Use the handy event callback
            document.addEventListener( "DOMContentLoaded", completed, false );

            // A fallback to window.onload, that will always work
            window.addEventListener( "load", completed, false );

        // If IE event model is used
        } else {
            // Ensure firing before onload, maybe late but safe also for iframes
            document.attachEvent( "onreadystatechange", completed );

            // A fallback to window.onload, that will always work
            window.attachEvent( "onload", completed );

            // If IE and not a frame
            // continually check to see if the document is ready
            var top = false;

            try {
                top = window.frameElement == null && document.documentElement;
            } catch(e) {}
　　　　　　　　
            if ( top && top.doScroll ) {
                (function doScrollCheck() {
                    if ( !jQuery.isReady ) {

                        try {
                            // Use the trick by Diego Perini
                            // http://javascript.nwbox.com/IEContentLoaded/
                            top.doScroll("left");
                        } catch(e) {
                            return setTimeout( doScrollCheck, 50 );
                        }

                        // detach all dom ready events
                        detach();

                        // and execute any waiting functions
                        jQuery.ready();
                    }
                })();
            }
        }
    }
    return readyList.promise( obj );
};

completed = function( event ) {

    // readyState === "complete" is good enough for us to call the dom ready in oldIE
    if ( document.addEventListener || event.type === "load" || document.readyState === "complete" ) {
        detach();
        jQuery.ready();
    }
},

ready: function( wait ) {

    // Abort if there are pending holds or we‘re already ready
    if ( wait === true ? --jQuery.readyWait : jQuery.isReady ) {
        return;
    }

    // Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
    if ( !document.body ) {
        return setTimeout( jQuery.ready );
    }

    // Remember that the DOM is ready
    jQuery.isReady = true;

    // If a normal DOM Ready event fired, decrement, and wait if need be
    if ( wait !== true && --jQuery.readyWait > 0 ) {
        return;
    }

    // If there are functions bound, to execute
    readyList.resolveWith( document, [ jQuery ] );

    // Trigger any bound ready events
    if ( jQuery.fn.trigger ) {
        jQuery( document ).trigger("ready").off("ready");
    }
},