总结
事件委托就是利用事件冒泡，只指定一个事件处理程序，就可以管理某一类型的所有事件
代码
<!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>事件委托</title>
</head>
<body>
<ul id="ul">
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ul>
<button id="btn">添加li</button>
</body>
<script>
// 事件委托弹框
let ul = document.querySelector('#ul')
ul.onclick = function (event) {
event = event || window.event
let target = event.target
if (target.nodeName === 'LI') {
alert(target.innerHTML)
}
}
let btn = document.querySelector('#btn')
btn.onclick = function () {
let li = document.createElement('li')
li.textContent = ul.children.length + 1
ul.appendChild(li)
}
</script>
</html>