<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<ul id="list">
<li>
111111111
<button>add</button>
</li>
</ul>
<script>
list.onclick = function(evt){
// 输出目标事件源
console.log(evt.target || evt.srcElement)
}
// 减少多个函数绑定的性能损耗
// 动态添加li 也会有事件处理
</script>
</body>
</html>