老外写的页面dom加载完成后执行的事件

window..onload的是页面加载完成后执行的事件，而且winodw.onload不能多次执行，jquery的$(fn)解决了这个问题，但是不使用jquery的情况下呢?以下是老外写的解决办法

/*
 * (c)2006 Jesse Skinner/Dean Edwards/Matthias Miller/John Resig
 * Special thanks to Dan Webb's domready.js Prototype extension
 * and Simon Willison's addLoadEvent
 *
 * For more info, see:
 * http://www.thefutureoftheweb.com/blog/adddomloadevent
 * http://dean.edwards.name/weblog/2006/06/again/
 * http://www.vivabit.com/bollocks/2006/06/21/a-dom-ready-extension-for-prototype
 * http://simon.incutio.com/archive/2004/05/26/addLoadEvent
 * 
 *
 * To use: call addDOMLoadEvent one or more times with functions, ie:
 *
 *    function something() {
 *       // do something
 *    }
 *    addDOMLoadEvent(something);
 *
 *    addDOMLoadEvent(function() {
 *        // do other stuff
 *    });
 *
 */
 
addDOMLoadEvent = (function(){
    // create event function stack
    var load_events = [],
        load_timer,
        script,
        done,
        exec,
        old_onload,
        init = function () {
            done = true;

            // kill the timer
            clearInterval(load_timer);

            // execute each function in the stack in the order they were added
            while (exec = load_events.shift())
                exec();

            if (script) script.onreadystatechange = '';
        };

    return function (func) {
        // if the init function was already ran, just run this function now and stop
        if (done) return func();

        if (!load_events[0]) {
            // for Mozilla/Opera9
            if (document.addEventListener)
                document.addEventListener("DOMContentLoaded", init, false);

            // for Internet Explorer
            /*@cc_on @*/
            /*@if (@_win32)
                document.write("<script id=__ie_onload defer src=//0><\/scr"+"ipt>");
                script = document.getElementById("__ie_onload");
                script.onreadystatechange = function() {
                    if (this.readyState == "complete")
                        init(); // call the onload handler
                };
            /*@end @*/

            // for Safari
            if (/WebKit/i.test(navigator.userAgent)) { // sniff
                load_timer = setInterval(function() {
                    if (/loaded|complete/.test(document.readyState))
                        init(); // call the onload handler
                }, 10);
            }

            // for other browsers set the window.onload, but also execute the old window.onload
            old_onload = window.onload;
            window.onload = function() {
                init();
                if (old_onload) old_onload();
            };
        }

        load_events.push(func);
    }
})();