数字字母验证
验证码：
<html>
<head>
<title>纯字验证码</title>
<meta http-equiv='content-type' content='text/html;charset=utf-8'/>
<script type='text/javascript' src='jquery-1.7.2.js'></script>
<script type='text/javascript'>
var code ; //在全局定义验证码
function createCode(){
code = "";
var codeLength = 4;//验证码的长度
var checkCode = document.getElementById("code");
var random = new Array(0,1,2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R',
'S','T','U','V','W','X','Y','Z');//随机数
for(var i = 0; i < codeLength; i++) {//循环操作
var index = Math.floor(Math.random()*36);//取得随机数的索引（0~35）
code += random[index];//根据索引取得随机数加到code上
}
checkCode.value = code;//把code值赋给验证码
}
//校验验证码
function validate(){
var inputCode = document.getElementById("input").value.toUpperCase(); //取得输入的验证码并转化为大写
if(inputCode.length <= 0) { //若输入的验证码长度为0
alert("请输入验证码！"); //则弹出请输入验证码
}else if(inputCode != code ) { //若输入的验证码与产生的验证码不一致时
alert("验证码输入错误！@_@"); //则弹出验证码输入错误
createCode();//刷新验证码
document.getElementById("input").value = "";//清空文本框
}else { //输入正确时
alert("合格！^-^");
}
}
</script>
<style type='text/css'>
#code{
font-family:Arial,宋体;
font-style:italic;
color:green;
border:0;
padding:2px 3px;
letter-spacing:3px;
font-weight:bolder;
}
</style>
</head>
<body onload='createCode()'>
<div>验证码：
<input type = "text" id = "input"/>
<input type="button" id="code" onclick="createCode()" style="60px" title='点击更换验证码' />
<input type = "button" value = "验证" onclick = "validate()"/>
</div>
</body>
</html>