<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<style>
#div1{width:400px;height:400px;background-color:blue;}
</style> <body>
<div id='div1'> </div>
<input type='button' value='big' onclick='big();' /><br/>
<input type='button' value='bigger' onclick='bigger();' />
<script>
function big(){
var div1=document.getElementById('div1');
div1.style.width=800; }
function bigger(){
var div1=document.getElementById('div1');
div1.style.width=100;
var width=div1.style.width || div1.clientWidth || div1.offsetWidth || div1.scrollWidth;
/*实际用div1.offsetWidth就够了，上边的麻烦了*/
alert(width);
} </script> </body> </html>