JS实现验证码

温馨提示：不推荐使用下面方法（及前端验证码校验）进行校验，因为只进行前台验证而不进行后台服务器端的校验，黑客大咖们很容易攻破这道防线，不能够很好的保证网站的安全性。
<!Doctype html>
<head>
    <title>js验证码</title>
    <style type="text/css">
        .code
        {
            font-family:Arial;
            font-style:italic;    /*字体倾斜*/
            color:blue;
            font-size:30px;
            border:0;
            padding:2px 3px;
            letter-spacing:3px;
            font-weight:bolder;
            float:left;
            cursor:pointer;
            width:150px;
            height:60px;
            line-height:60px;
            text-align:center;
            vertical-align:middle;
        }
        a
        {
            text-decoration:none;
            font-size:12px;
            color:#288bc4;
        }
        a:hover
        {
            text-decoration:underline;
        }
        /*td{
            border: 1px solid black;
            box-sizing: border-box;
         }
        td:nth-child(1){
            width: 78px;
        }*/
    </style>
    <script type="text/javascript">
        var code;  //定义一个变量，用来保存验证码
        //生成验证码
        function createCode() {
            code = "";
            var codeLength = 6; //验证码的长度
            var checkCode = document.getElementById("checkCode");
            var codeChars = 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',
                '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 charNum = Math.floor(Math.random() * 51);
                code += codeChars[charNum];
            }
            if(checkCode) {
                checkCode.innerHTML = code;
            }
        }
        //校验验证码
        function validateCode() {
            var inputCode=document.getElementById("inputCode").value;
            console.log(inputCode);
            if(inputCode.length <= 0) {
                alert("请输入验证码！");
            }
            //toUpperCase() 方法用于把字符串转换为大写
            else if(inputCode.toUpperCase() != code.toUpperCase()) {
                alert("验证码输入有误！");
                createCode();
            }
            else {
                alert("验证码正确！");
            }
        }
    </script>
</head>
<body "createCode()">
<form id="form1" runat="server" "validateCode()">
    <div>
        <table border="0" cellspacing="5" cellpadding="5" >
            <tr>
                <td></td>
                <td><div class="code" id="checkCode" "createCode()" ></div></td>
                <td><a href="#" "createCode()">看不清换一张</a></td>
            </tr>
            <tr>
                <td>验证码：</td>
                <td><input style="float:left;" type="text"  id="inputCode" /></td>
                <td>请输入验证码</td>
            </tr>
            <tr>
                <td></td>
                <td><input id="Button1" "validateCode()" type="button" value="确定" /></td>
                <td></td>
            </tr>
        </table>
    </div>
</form>
</body>
</html>
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