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利用事件冒泡，将子级的事件委托给父级加载
利用事件函数中 e 参数，内部存储的是事件对象

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        li{
            padding-left: 20px;
            cursor: pointer;
        }
        ul{margin: 50px auto;
        font-size: 24px;
        line-height: 48px;
        list-style: note;
        }
    </style>
</head>
<body>
    <ul id="list">
        <li>是是是</li>
        <li>去去去</li>
        <li>嘻嘻嘻</li>
        <li>哦哦哦</li>
    </ul>

    <script>
        var list = document.getElementById("list");
        var lis = list.children;
        //给ul添加点击事件
        list.onclick = function(e){
            
            for(var i = 0; i < lis.length; i++){
                lis[i].style.backgroundColor = "";
            }
            e.target.style.backgroundColor = "pink";

        };


    </script>
</body>
</html>