firefox中addEventListener()方法和ie中attachEvent()方法都是为HTML元素添加一个事件监听
为什么要采用事件监听而不是直接对元素的事件属性（如：onclick、onmouseover）赋值？
这两种方法处理事件还是有很大区别的！事件属性只能赋值一种方法，即：
button1.onclick = function() { alert(1); };
button1.onclick = function() { alert(2); };
这样后面的赋值语句就将前面的onclick属性覆盖了。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Coda Bubble Example</title>
</head>
<body>
<button id="Button1">测试</button>
<script type="text/javascript">
/// <summary>
/// 添加事件监听
/// </summary>
/// <param name="target">载体</param>
/// <param name="type">事件类型</param>
/// <param name="func">事件函数</param>
function addEventHandler(target, type, func) {
if (target.addEventListener)
target.addEventListener(type, func, false);
else if (target.attachEvent)
target.attachEvent("on" + type, func);
else target["on" + type] = func;
}
/// <summary>
/// 移除事件监听
/// </summary>
/// <param name="target">载体</param>
/// <param name="type">事件类型</param>
/// <param name="func">事件函数</param>
function removeEventHandler(target, type, func) {
if (target.removeEventListener)
target.removeEventListener(type, func, false);
else if (target.detachEvent)
target.detachEvent("on" + type, func);
else delete target["on" + type];
}
var Button1 = document.getElementById("Button1");
var Button1Click = function() { alert(1); };
addEventHandler(Button1, "click", Button1Click);
addEventHandler(Button1, "click", function() { alert(2); } );
addEventHandler(Button1, "click", function() { alert(3); } );
removeEventHandler(Button1, "click", function() { alert(2); } ); // 移不出
removeEventHandler(Button1, "click", Button1Click); // 可以移除
</script>
</body>
</html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Coda Bubble Example</title>
</head>
<body>
<button id="Button1">测试</button>
<script type="text/javascript">
/// <summary>
/// 添加事件监听
/// </summary>
/// <param name="target">载体</param>
/// <param name="type">事件类型</param>
/// <param name="func">事件函数</param>
function addEventHandler(target, type, func) {
if (target.addEventListener)
target.addEventListener(type, func, false);
else if (target.attachEvent)
target.attachEvent("on" + type, func);
else target["on" + type] = func;
}
/// <summary>
/// 移除事件监听
/// </summary>
/// <param name="target">载体</param>
/// <param name="type">事件类型</param>
/// <param name="func">事件函数</param>
function removeEventHandler(target, type, func) {
if (target.removeEventListener)
target.removeEventListener(type, func, false);
else if (target.detachEvent)
target.detachEvent("on" + type, func);
else delete target["on" + type];
}
var Button1 = document.getElementById("Button1");
var Button1Click = function() { alert(1); };
addEventHandler(Button1, "click", Button1Click);
addEventHandler(Button1, "click", function() { alert(2); } );
addEventHandler(Button1, "click", function() { alert(3); } );
removeEventHandler(Button1, "click", function() { alert(2); } ); // 移不出
removeEventHandler(Button1, "click", Button1Click); // 可以移除
</script>
</body>
</html>
而添加事件监听就可以并行。
特别是当团队合作时，事件并行的需求增多，比如：监听document对象的鼠标事件或者window对象的载入事件等。
使用事件属性则很容易造成事件覆盖掉。
经过测试IE(8)中先显示3再显示2，而firefox(3)中则先显示2再显示3
这个是为什么呢？测试的结果即真理，没啥好想的。囧
