js效果，onclick，还有getElementsByClassName的用法和style用法
<!DOCTYPE html>
<html>
<head>
<title>JS事件</title>
</head>
<style type="text/css">
*{margin:0;padding:0;}
.m{width:100px; height:100px;border:1px solid #999;}
</style>
<body>
<div class="m" onclick="change()">
</div>
<script type="text/javascript">
function change(){
var m=document.getElementsByClassName('m')[0];
m.style.background = 'red';
}
</script>
</body>
</html>