<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>mapDr2</title>
<style>
.btns_mapDr{
color: red;
border-color: #66ccff;
border-style:dotted;
border-width:3px;
}
.btns_mapDr:hover{
cursor: pointer;
}
</style>
</head>
<body>
<table>
<tr>
<td class="btns_mapDr mapDrbili" id="mapDrbili" mapURL-data="http://www.bilibili.com/video/kichiku.html">鬼畜区</td>
<td class="btns_mapDr mapDracfun" id="mapDracfun" mapURL-data="http://www.bilibili.com/video/teleplay.html">影视区</td>
</tr>
</table>
<iframe id="mapFrame" width="100%" height="800" src ="https://www.bilibili.com/"></iframe>
</body>
<script type="text/javascript">
var btns = document.getElementsByClassName("btns_mapDr");
btns.onclick = function () {
alert("hello");
}
</script>
</html>因为你这个还没有获取id