js事件捕获冒泡
程序员文章站
2022-07-14 09:30:01
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浏览器在发生一个事件时会从经过顶层到目标的捕获过程，目标到顶层的冒泡过程，不多解释，看代码理解
<html>
<head>
<style>
#outer{
width: 200px;
height: 200px;
background: #F08738;
}
#mid{
width: 150px;
height: 150px;
background: #293484;
}
#inner{
width: 100px;
height: 100px;
background: #783948;
}
#target{
width: 50px;
height: 50px;
background: #98fe99;
}
</style>
</head>
<body>
<div id="outer">
<div id="mid">
<div id="inner">
<div id="target"></div>
</div>
</div>
</div>
<script>
var o = document.getElementById('outer');
var m = document.getElementById('mid');
var i = document.getElementById('inner');
var t = document.getElementById('target');
</script>
</body>
</html>
四个div层次很清楚
下面为div绑定事件
o.addEventListener('click', function(){console.log('outer')});
m.addEventListener('click', function(){console.log('mid')});
i.addEventListener('click', function(){console.log('inner')});
t.addEventListener('click', function(){console.log('target')});
点击target的结果如下，依次输出target inner mid outer
冒泡的结果，点击target, 它父层的div的click事件也会执行
再看捕获阶段
o.addEventListener('click', function(){console.log('outer')}, true);
m.addEventListener('click', function(){console.log('mid')}, true);
i.addEventListener('click', function(){console.log('inner')}, true);
t.addEventListener('click', function(){console.log('target')}, true);
addEventListener最后加了个参数，指明此事件在捕获阶段执行，其结果是 outer mid inner target
可以看出来从顶层到目标元素的捕获阶段
捕获，冒泡一起绑定
o.addEventListener('click', function(){console.log('outer bubble')}, false);
o.addEventListener('click', function(){console.log('outer')}, true);
m.addEventListener('click', function(){console.log('mid bubble')}, false);
m.addEventListener('click', function(){console.log('mid')}, true);
i.addEventListener('click', function(){console.log('inner bubble')}, false);
i.addEventListener('click', function(){console.log('inner')}, true);
t.addEventListener('click', function(){console.log('target bubble')}, false);
t.addEventListener('click', function(){console.log('target')}, true);
点击target结果是
outer
mid
inner
target bubble
target
inner bubble
mid bubble
outer bubble
可以看到先是执行捕获阶段的函数，然后是冒泡阶段的函数
对于目标元素target没有捕获冒泡区分，指定冒泡阶段的函数在指定捕获阶段的函数先执行了。执行顺序不确定
