介绍JavaScript正则实现表达式以字母开头-木庄网络博客

本文摘自PHP中文网，作者coldplay.xixi，侵删。

免费学习推荐：javascript视频教程

表单校验:创建表单,使用JavaScript+dom为表单添加校验.

要求:

验证用户名称,必须以字母开头,长度2-6位之间.
验证密码不能为空.
确认密码不能为空,要与密码一致.

<!DOCTYPE html><html lang="en"><!-- 表单校验:创建表单,使用JavaScript为表单添加校验.
    1.验证用户名称,必须以字母开头,长度2-6位之间.
    2.验证密码不能为空.
    3.确认密码不能为空,要与密码一致. --><head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script type="text/javascript">
        function checkForm() {
            //获得用户名对象
            var username = document.getElementById("username");
            //---获得用户名输入框中的value值
            var usernamevalue = username.value;
            var Reg = /^[a-zA-Z][-_a-zA-Z0-9]{1,5}/;//JavaScript中的正则与Java的正则略有不同
            if (usernamevalue.length >= 2 && usernamevalue.length <= 6 && Reg.test(usernamevalue)) {
                //为span设置提示语
                document.getElementById("usernameSpan").innerHTML = "<font color='green'> 用户名可用<font>";
            } else {
                document.getElementById("usernameSpan").innerHTML = "<font color='red'> 用户名必须以字母开头且长度在2-6之间<font>";
            }
 
            //获得密码value
            var password = document.getElementById("password").value;
            if (password == "") {
                document.getElementById("passwordSpan").innerHTML = "<font color='red'>密码不能为空</font>";
            } else {
                document.getElementById("passwordSpan").innerHTML = "<font color='green'>密码可用</font>";
            }
 
            //获得确认密码
            var repassword = document.getElementById("repassword").value;
 
            if (repassword == password) {
                document.getElementById("repasswordSpan").innerHTML = "<font color='green'>输入一致</font>";
            } else {
                document.getElementById("repasswordSpan").innerHTML = "<font color='red'>两次输入密码不一致</font>";
            }
        }
    </script></head><body>
    <h2>新用户注册</h2>
    <p style="border: 1px solid sandybrown; width: 300px; height: 260px;">
        <form action="">
            <table cellspacing="15">
                <tr>
                    <td>
                        用户名称:
                    </td>
                    <td>
                        <input type="text" id="username">
                        <span id="usernameSpan"></span>
                    </td>
 
                </tr>
 
                <tr>
                    <td>
                        密&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp码:
                    </td>
                    <td>
                        <input type="password" id="password">
                        <span id="passwordSpan"></span>
                    </td>
 
                </tr>
 
                <tr>
                    <td>
                        确认密码:
                    </td>
                    <td>
                        <input type="password" id="repassword">
                        <span id="repasswordSpan"></span>
                    </td>
                </tr>
            </table>
        </form>
    </p>
    <input type="button" value="确认注册" onclick="checkForm()" /></body></html>