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);   
			code +=selectChar[charIndex];   
       }      
       if(checkCode)   
       {   
         checkCode.className="code";   
         checkCode.value = code;   
       }   
          
     }   
        
      function validate ()   
      {   
       var inputCode = document.getElementById("yanzhengma").value;   
       if(inputCode.length <=0)   
       {   
           alert("请输入验证码！");
           return false;   
       }   
       else if(inputCode != code )   
       {   
          alert("验证码输入错误！");   
          createCode();//刷新验证码   
          return false;
       }   
       else   
       {  
         return true;
       }   
          
       }