老师这样对吗

来源：7-2 编程练习

为爱修行

2019-02-28 16:28:46

<!DOCTYPE html>
<html>

<head>
    <title></title>
    <style type="text/css">
    html,
    body {
        margin: 0;
        padding: 0;
    }

    div:not(:nth-of-type(2)) {
        width: 500px;
        height: 100%;
        background-color: #00c4ff7a;
        margin: 0 auto;
    }
    /*ul默认有外边距*/

    ul {
        width: 300px;
        height: 100%;
        background-color: #f9c3e6d6;
        list-style: none;
        /*清除默认边距*/
        margin: 0;
        padding: 0;
        margin: 20px auto;
        margin-bottom: 30px;
    }

    li {
        width: 200px;
        height: 30px;
        line-height: 30px;
        margin: 30px auto;
        background-color: #cdffc0;
    }
    </style>
</head>

<body>
    <div id="box">
        <button id="btnAdd">添加元素</button>
        <button id="btnRemove">删除元素</button>
        <ul id="list">我是ul
            <li>我是li1</li>
            <li>我是li2</li>
            <li>我是li3</li>
        </ul>
    </div>
    <script type="text/javascript">
    //此处填写代码
        (function(){
            var wrap={
                list:document.querySelector('#list'),
                li:document.querySelectorAll('li'),
                btnAdd:document.getElementById('btnAdd'),
                btnRemove:document.getElementById('btnRemove')
            };

            for (var i = 0; i < wrap.li.length; i++) {
                wrap.li[i].onmouseover=function(){
                    this.style.background='purple';
                }
                wrap.li[i].onmouseout=function(){
                    this.style.background='pink';
                }
            }

            wrap.btnAdd.onclick=function(){
                var len=wrap.list.childElementCount;
                var newLi=document.createElement('li');
                var txt=document.createTextNode('我是li'+(len+1));
                newLi.appendChild(txt);
                wrap.list.appendChild(newLi);
            }

            wrap.btnRemove.onclick=function(){
                if(wrap.list.childElementCount>0){
                    wrap.list.removeChild(list.lastElementChild);
                }
            }
        })();
    </script>
</body>

</html>

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