obj = document.getElementById("testdiv");
obj.onclick=function(){alert('1');};
obj.onclick=function(){alert('2');};
obj.onclick=function(){alert('3');};
// 当使用上边三句话进行事件绑定的时候，很明显当点击ID为testdiv对象时，只能执行
//最后一句脚本。因为onclick作为一个事件处理对象，只能赋一个值，后面的赋值自动覆
//盖前面的

obj = document.getElementById("testdiv");
obj.attachEvent('onclick',function(){{alert('1');});
obj.attachEvent('onclick',function(){{alert('2');});
obj.attachEvent('onclick',function(){{alert('3');});//点击时，三个方法都会执行

obj = document.getElementById("testdiv");
obj.addEventListener('click',function(){{alert('1');},false);
obj.addEventListener('click',function(){{alert(2');},false);
obj.addEventListener('click',function(){{alert('3');},false);//点击时，三个方法都会执行

obj = document.getElementById("testdiv");
obj.attachEvent('onclick',function(){{alert('1');});
obj.attachEvent('onclick',function(){{alert('2');});
obj.attachEvent('onclick',function(){{alert('3');});
//执行顺序是alert(3),alert(2),alert(1);

obj = document.getElementById("testdiv");
obj.addEventListener('click',function(){{alert('1');},false);
obj.addEventListener('click',function(){{alert('2');},false);
obj.addEventListener('click',function(){{alert('3');},false);
//点击obj对象时,执行顺序为alert('1'),alert('2'),alert('3');

function addEvent(elm, evType, fn, useCapture) 
{if (elm.addEventListener) {// W3C标准elm.addEventListener(evType, fn, useCapture);return true;}else if (elm.attachEvent) {//IEvar r = elm.attachEvent(‘on‘   evType, fn);//IE5 return r;}else {elm['on'   evType] = fn;//DOM事件}
}

        function addEvent(element, type, handler) {//为每一个事件处理函数分派一个唯一的IDif (!handler.$$guid) handler.$$guid = addEvent.guid  ;//为元素的事件类型创建一个哈希表if (!element.events) element.events = {};//为每一个"元素/事件"对创建一个事件处理程序的哈希表var handlers = element.events[type];if (!handlers) {handlers = element.events[type] = {};//存储存在的事件处理函数(如果有)if (element["on"   type]) {handlers[0] = element["on"   type];}}//将事件处理函数存入哈希表handlers[handler.$$guid] = handler;//指派一个全局的事件处理函数来做所有的工作element["on"   type] = handleEvent;};//用来创建唯一的ID的计数器addEvent.guid = 1;function removeEvent(element, type, handler) {//从哈希表中删除事件处理函数if (element.events && element.events[type]) {delete element.events[type][handler.$$guid];}};function handleEvent(event) {var returnValue = true;//抓获事件对象(IE使用全局事件对象)event = event || fixEvent(window.event);//取得事件处理函数的哈希表的引用var handlers = this.events[event.type];//执行每一个处理函数for (var i in handlers) {this.$$handleEvent = handlers[i];if (this.$$handleEvent(event) === false) {returnValue = false;}}return returnValue;};//为IE的事件对象添加一些“缺失的”函数function fixEvent(event) {//添加标准的W3C方法event.preventDefault = fixEvent.preventDefault;event.stopPropagation = fixEvent.stopPropagation;return event;};fixEvent.preventDefault = function () {this.returnValue = false;};fixEvent.stopPropagation = function () {this.cancelBubble = true;};

var addEvent = (function () {if (document.addEventListener) {return function (el, type, fn) {if (el.length) {for (var i = 0; i && el.length; i  ) {addEvent(el[i], type, fn);}} else {el.addEventListener(type, fn, false);}};} else {return function (el, type, fn) {if (el.length) {for (var i = 0; i && el.length; i  ) {addEvent(el[i], type, fn);}} else {el.attachEvent('on'   type, function () {return fn.call(el, window.event);});}};}})();