js编写验证码

这是一个简单的js编写的验证码，自己已经亲自验证，没有问题了
 <!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>

 <title>js编写验证码</title>

     <style type="text/css" >  

         .code

         {

             background-image:url(code.jpg);

             font-family:Arial;

             font-style:italic;

             color:Red;

             border:0;

             padding:2px 3px;

             letter-spacing:3px;

             font-weight:bolder;

         }   

         .unchanged

         {

             border:0;

         }

     </style>

     <script language="javascript" type="text/javascript">

      var code ; //在全局 定义验证码

      function createCode()

      {

        code = "";

        var codeLength = 6;//验证码的长度

        var checkCode = document.getElementById("checkCode");

        var selectChar = 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');//所有候选组成验证码的字符，当然也可以用中文的

        for(var i=0;i<codeLength;i++)

        {   

        var charIndex = Math.floor(Math.random()*36);   //Math.random得到0-36中随机的一个数,floor取整数部分

        code +=selectChar[charIndex];

        }

 //       alert(code);

        if(checkCode)

        {

          checkCode.className="code";

          checkCode.value = code;

        }

      }   

       function validate ()

      {   

        var inputCode = document.getElementById("input1").value;

        if(inputCode.length <=0)

        {

            alert("请输入验证码！");

        }

        else if(inputCode != code )

        {

          alert("验证码输入错误！");

           createCode();//刷新验证码

        }

        else

        {

          alert("^-^ OK");

        }   

      }   

     </script>

 </head>

 <body onload="createCode()" >

 <form  action="#">

   <input  type="text"   id="input1" />

 <input type="text" onclick="createCode()" readonly="readonly" id="checkCode" class="unchanged" style="width: 80px"  /><br />  

     <input id="Button1"  onclick="validate();" type="button" value="确定" />    

 </form>

 </body>

 </html>
一定要在body出onload不然第一次加载的时候看不到验证码
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