<!DOCTYPE html><html>?? ?<head>?? ??? ?<meta charset="UTF-8">?? ??? ?<title></title>?? ??? ?<style>?? ??? ??? ?ul{?? ??? ??? ??? ?position: relative;?? ??? ??? ??? ?list-style: none;?? ??? ??? ?}?? ??? ??? ?ul li{?? ??? ??? ??? ?width: 100px;?? ??? ??? ??? ?height: 50px;?? ??? ??? ??? ?background: #CCCCCC;?? ??? ??? ??? ?margin: 2px;?? ??? ??? ?}?? ??? ??? ?div{?? ??? ??? ??? ?width: 200px;?? ??? ??? ??? ?height: 200px;?? ??? ??? ??? ?background: greenyellow;?? ??? ??? ??? ?position: absolute;?? ??? ??? ??? ?top: 0px;?? ??? ??? ??? ?left: 150px;?? ??? ??? ??? ?display: block;?? ??? ??? ?}?? ??? ?</style>?? ??? ?<script>?? ??? ??? ?window.onload=function(){?? ??? ??? ??? ?var oUl=document.getElementsByTagName("ul")[0];?? ??? ??? ??? ?var oLi=document.getElementsByTagName("li");?? ??? ??? ??? ?var oDiv=document.getElementsByTagName("div")[0];?? ??? ??? ??? ?for (var i=0;i<oLi.length;i++) {?? ??? ??? ??? ??? ?oLi[i].onmousemove=function(){?? ??? ??? ??? ??? ??? ?if (oUl.offsetHeight-oLi[i].offsetTop>200) {?? ??? ??? ??? ??? ??? ??? ?oDiv.style.top=oLi[i].offsetTop+"px";?? ??? ??? ??? ??? ??? ??? ?oDiv.style.display="block";?? ??? ??? ??? ??? ??? ?}?? ??? ??? ??? ??? ??? ?else{?? ??? ??? ??? ??? ??? ??? ?oDiv.style.top=this.offsetTop+oLi[i].offsetHeight-200+"px";?? ??? ??? ??? ??? ??? ?}?? ??? ??? ??? ??? ??? ??? ??? ??? ??? ?}?? ??? ??? ??? ?}?? ??? ??? ?}?? ??? ?</script>?? ?</head>?? ?<body>?? ??? ?<ul>?? ??? ??? ?<li>1111</li>?? ??? ??? ?<li>2222</li>?? ??? ??? ?<li>3333</li>?? ??? ??? ?<li>4444</li>?? ??? ??? ?<li>5555</li>?? ??? ??? ?<li>6666</li>?? ??? ??? ?<li>7777</li>?? ??? ??? ?<li>8888</li>?? ??? ??? ?<li>9999</li>?? ??? ??? ?<li>1010</li>?? ??? ??? ?<div></div>?? ??? ?</ul>?? ?</body></html>這個程序運行為什么會報錯---Cannot read property 'offsetTop' of undefined"？但是把oLi【i】改成this反而可以運行為什么會這樣
一個原生js的新手問題--和this有點關系
肖小波
2016-12-08 19:34:48
