随机码生成

<script language="javascript" 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("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);   
	       code +=selectChar[charIndex];   
       }     
       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");   
	       }   
      }   
      window.onload=createCode;
</script>