js生成验证码并直接在前端判断

  <script type="text/javascript" src="img/jquery-1.5.1.min.js"></script>

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



    var code; //在全局 定义验证码

    var code2; //在全局 定义验证码

    function createCode() {

      code = "";

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

      function RndNum(n) {

        var rnd = "";

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

          rnd += Math.floor(Math.random() * 10);

        return rnd;

      }



      var num = RndNum(2);

      var num2 = RndNum(2);



      code = num + "+" + num2 + "=";

      code2 = parseInt(num) + parseInt(num2)



      if (checkCode) {

        checkCode.className = "code";

        checkCode.value = code;

      }



    }

  </script>

  <script type="text/javascript">

    $(document).ready(function () {



      $("#input1").blur(function () {

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

        if (inputCode.length <= 0) {

          alert("请输入验证码！");

        }

        else if (inputCode != code2) {

          alert("验证码输入错误！");

          createCode(); //刷新验证码

        }

        else {

          alert("^-^ OK");

        }

      });

    })

  </script>

 <form action="#">

   <input type="text" id="input1" />

  <input type="text" onclick="createCode()" readonly="readonly" id="checkCode" class="unchanged" style="width: 80px;background: #660099"/><br />

  </form> 

<style type="text/css">

    .code

    {

      font-family: Arial;

      font-style: italic;

      color: Red;

      border: 0;

      padding: 2px 3px;

      letter-spacing: 3px;

      font-weight: bolder;

    }

    .unchanged

    {

      border: 0;

    }

  </style>