js生成验证码并且验证

    <html>  
        <head>  
            <title>验证码</title>  
            <style type="text/css">  
                #code  
                {  
                    font-family:Arial;  
                    font-style:italic;  
                    font-weight:bold;  
                    border:0;  
                    letter-spacing:2px;  
                    color:blue;  
                }  
            </style>  
            <script type = "text/javascript" src = "checkCode.js">  
            </script>  
        </head>  
        <body>  
            <div>  
                <input type = "text" id = "input"/>  
                <input type = "button" id="code" onclick="createCode()"/>  
                <input type = "button" value = "验证" onclick = "validate()"/>  
            </div>  
        </body>  
    </html>

checkCode.js

var code ; //在全局定义验证码   
//产生验证码  
window.onload = createCode;
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("^-^"); //弹出^-^  
    }             
}