jquery里有专门解决DOM加载的函数$(document).ready()（简写就是$(fn)），非常好用！John Resig在《Pro JavaScript Techniques》里，有这样一个方法处理DOM加载，原理就是通过document&& document.getElementsByTagName &&document.getElementById&& document.body 去判断Dom树是否加载完毕。代码如下：
代码:
function domReady( f ) {
// 如果DOM加载完毕，马上执行函数
if ( domReady.done ) return f();  
// 假如我们已增加一个函数
if ( domReady.timer ) {
// 把它加入待执行的函数清单中
domReady.ready.push( f );
} else {
// 为页面加载完成绑定一个事件,
// 为防止它最先完成. 使用 addEvent（下面列出）.
addEvent( window, “load”, isDOMReady );  
// 初始化待执行的函数的数组
domReady.ready = [ f ];  
// 经可能快地检查Dom是否已可用
domReady.timer = setInterval( isDOMReady, 13 );
}
} 
// 检查Dom是否已可操作
function isDOMReady() {
// 假如已检查出Dom已可用, 忽略
if ( domReady.done ) return false;  
// 检查若干函数和元素是否可用
if ( document &&  document.getElementsByTagName &&  document.getElementById &&  document.body ) {  
// 假如可用, 停止检查
clearInterval( domReady.timer );
domReady.timer = null;  
// 执行所有等待的函数
for ( var i = 0; i < domReady.ready.length; i++ )
domReady.ready[i]();  
// 记录在此已经完成
domReady.ready = null;
domReady.done = true;
}
}
// 由 Dean Edwards 在2005 所编写addEvent/removeEvent,
// 由 Tino Zijdel整理
//
//优点是1.可以在所有浏览器工作；
//2.this指向当前元素；
//3.综合了所有浏览器防止默认行为和阻止事件冒泡的的函数
//缺点就是仅在冒泡阶段工作
function addEvent(element, type, handler) {
    // assign each event handler a unique ID
    if (!handler.$$guid) handler.$$guid = addEvent.guid++;
    // create a hash table of event types for the element
    if (!element.events) element.events = {};
    // create a hash table of event handlers for each element/event pair
    var handlers = element.events[type];
    if (!handlers) {
        handlers = element.events[type] = {};
        // store the existing event handler (if there is one)
        if (element["on" + type]) {
            handlers[0] = element["on" + type];
        }
    }
    // store the event handler in the hash table
    handlers[handler.$$guid] = handler;
    // assign a global event handler to do all the work
    element["on" + type] = handleEvent;
};
// a counter used to create unique IDs
addEvent.guid = 1;
function removeEvent(element, type, handler) {
    // delete the event handler from the hash table
    if (element.events && element.events[type]) {
        delete element.events[type][handler.$$guid];
    }
};
function handleEvent(event) {
    var returnValue = true;
    // grab the event object (IE uses a global event object)
    event = event || fixEvent(window.event);
    // get a reference to the hash table of event handlers
    var handlers = this.events[event.type];
    // execute each event handler
    for (var i in handlers) {
        this.$$handleEvent = handlers[i];
        if (this.$$handleEvent(event) === false) {
            returnValue = false;
        }
    }
    return returnValue;
};
function fixEvent(event) {
    // add W3C standard event methods
    event.preventDefault = fixEvent.preventDefault;
    event.stopPropagation = fixEvent.stopPropagation;
    return event;
};
fixEvent.preventDefault = function() {
    this.returnValue = false;
};
fixEvent.stopPropagation = function() {
    this.cancelBubble = true;
};

还有一个估计由几个外国大师合作写的，实现同样功能。
代码:
/*
* (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:
*
*
*
*
*
*
* To use: call addDOMLoadEvent one or more times with functions, ie:
*
*    function something() {
*       // do something
*    }
*    addDOMLoadEvent(something);
*
*    addDOMLoadEvent(function() {
*        // do other stuff
*    });
*
*/