js生成六位验证码！

Html：

<form id="form1" runat="server" onsubmit="validateCode()">
    <div>
        <table border="0" cellspacing="5" cellpadding="5" >
            <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"  onclick="validateCode();" type="button" value="确定" /></td><td></td>
            </tr>
            <tr>
                <td></td><td> <div class="code" id="checkCode" onclick="createCode()" ></div></td>
                <td><a  href="#" onclick="createCode()">换一张</a></td>
            </tr>
        </table>
    </div>
</form>

Css：

<style>
    .code
    {
        background-color: #1cbb9b;
        font-family:Arial;
        font-style:italic;
        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;
    }
</style>

Javascript:

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

    var code;
    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() * 61);
            code += codeChars[charNum];
        }
        if (checkCode)
        {
            checkCode.className = "code";
            checkCode.innerHTML = code;
        }
    }
    function validateCode()
    {
        var inputCode = document.getElementById("inputCode").value;
        if (inputCode.length <= 0)
        {
            alert("请输入验证码！");
        }
        else if (inputCode.toUpperCase() != code.toUpperCase())
        {
            alert("验证码输入有误！");
            createCode();
        }
        else
        {
            alert("验证码正确！");
        }
    }
</script>