<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>test</title>
<style>
body{
padding: 0;
margin: 0; }
#box{
width: 200px;
height: 0;
background: #00f;
overflow: hidden; }
</style>
<script>
window.onload = function(){
var box = document.getElementById('box');
var btn = document.getElementById('btn');
btn.onclick = function(){
var height = box.offsetHeight;
if(height == 0){
box.style.height = 100+'px';
}else{
box.style.height = 0; }
}
}
</script>
</head>
<body>
<div id="box">
<h2>Hello World</h2>
</div>
<button id="btn">点击展开关闭</button>
</body>
</html>
