冒泡事件
js中“冒泡事件(bubble)”并不是能实际使用的花哨技巧,它是一种对js事件执行顺序的机制,“冒泡算法”在编程里是一个经典问题,冒泡算法里面的“冒泡”应该说是交换更加准确;js里面的“冒泡事件”才是真正意义上的“冒泡”,它从DOM最低层逐层遍历树,然后附加相应事件。以下面代码为例:
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<title>冒泡事件</title>
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<script type="text/javascript">
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function Add(sText)
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{
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document.getElementById("Console").innerHTML +=sText;
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}
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</script>
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</head>
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<body onclick="Add(’body事件触发<br />’)">
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<div onclick="Add(’div事件触发<br />’)">
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<p onclick="Add(’p事件触发<br />’)" style="background:#c00;">点击</p>
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</div>
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<div id="Console" style="border:solid 1px #ee0; background:#ffc;"></div>
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</body>
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事件监听
事件监听准确一点讲可以说是js引擎对用户鼠标、键盘、窗口事件等动作的监视进行的操作,也就是针对用户相应的操作进行附加事件,常用的类似 btnAdd.onclick="alert(’51obj.cn’)"就是一种简单的附加事件,只不过这种方法不支持附加多个事件以及删除事件。以下代 码将实现附加事件后删除事件(IE下):
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<script type="text/javascript">
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<!–
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var oP;
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function window.onload(){
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oP=document.getElementById("pContent");
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oP.attachEvent("onclick",Click);
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}
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function Click(){
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alert("做点什么吧");
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oP.detachEvent("onclick",Click);
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}
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//–>
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</script>
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</head>
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<body>
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<p id="pContent" style="border:solid 1px #d00; background:#cff;">点击</p>
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IE不能称为标准的DOM浏览器,即使是最新的IE8,相对于标准DOM如Firefox、Opera等,它是个“异类”;在Firefox中才真正有称为事件监听的函数addEventListener,如下例
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<script type="text/javascript">
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<!–
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window.onload=function(){
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var oBtn=document.getElementById("btn");
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oBtn.addEventListener("click",Click,false);
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}
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function Click(){
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alert("触发click事件");
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}
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//–>
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</script>
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<button id="btn">点击</button>
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从上面两个例子看出attachEvent在Firefox中并不支持,IE也不支持addEventListener.因此需要使用兼容性的方法。
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<script type="text/javascript">
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<!–
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var oBtn;
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window.onload=function(){
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oBtn=document.getElementById("btn");
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if(window.addEventListener){
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oBtn.addEventListener("click",Click,false);
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}//FF,Opera…
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else if(window.attachEvent){
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oBtn.attachEvent("onclick",Click,false);
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}//IE
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else{
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oBtn.onclick=Click;
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}//Other
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}
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function Click(){
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alert("事件只执行一次");
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if(window.addEventListener){
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oBtn.removeEventListener("click",Click,false);
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}//FF
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else if(window.attachEvent){
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oBtn.detachEvent("onclick",Click);
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}
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else{
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oBtn.onclick=null;
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}
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}
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//–>
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</script>
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</head>
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<body>
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<button id="btn">www.51obj.cn»»</button>
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</body>
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