<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<style>
#yard{
width: 530px;
height:200px;
font-size: 170px;
margin: 150px auto;
}
</style>
<body>
<div id="yard"></div>
<script>
var div = document.getElementById("yard");
var timer=setInterval(function(){
var strCode = ‘abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789‘;
var str = ‘‘;
while (str.length < 6) {
var str1 = strCode.charAt(Math.round(Math.random() * 61));
if (str.indexOf(str1) === -1) {
str += str1;
}
}
div.innerHTML=str;
},1000)
</script>
</body>
</html>
原文：http://www.cnblogs.com/qiancheng123/p/6337492.html