javascript实现数字+字母验证码的简单实例

实例如下：
复制代码代码如下:
<！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>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
    <title>js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 = 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","wW","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];


       }
//       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>