<html>
<head>
<script type="text/javascript">
num=0
function a(){
for(i=0;i<=100;i++)
{
if(i%2==0)
num+=i;
}
alert(num);
}
</script>
</head>
<body>
<input type="button" value="click me"
onclick="a()"/>
</body>
</html>
<input type="button" value="click me"
onclick="a()"/>
</body>
</html>
原文：http://www.cnblogs.com/hhhhg/p/7894764.html