JavaScript验证密码强度

JavaScript的方法：

    <script type="text/javascript">
        window.onload = function () {
            document.getElementById('txt').onkeydown = function () {

                //获取td
                var tds = document.getElementById('tb').getElementsByTagName('td');
                for (var i = 0; i < tds.length; i++) {
                    tds[i].style.backgroundColor = '#E6E6E6';
                }

                var pwd = this.value; //获取密码
                if (pwd.length > 0) {
                    var result = getPassWord(pwd);
                    if (result <= 1) {
                        //弱
                        tds[0].style.backgroundColor = 'red';
                    } else if (result == 2) {
                        //中
                        tds[0].style.backgroundColor = 'orange';
                        tds[1].style.backgroundColor = 'orange';
                    } else if (result == 3) {
                        //强
                        tds[0].style.backgroundColor = 'green';
                        tds[1].style.backgroundColor = 'green';
                        tds[2].style.backgroundColor = 'green';
                    }

                }
            }
        }
        //利用正则表达式匹配相关字符串,返回密码的强度值
        function getPassWord(pwdMsg) {
            var lvl = 0;
            /*
            var reg = /d/;
            if (reg.test(pwdMsg)) {
            lvl++;
            };
            */
            //密码中有数字加1
            if (pwdMsg.match(/d/)) {
                lvl++;
            }
            //密码中有字符加1
            if (pwdMsg.match(/[a-zA-Z]/)) {
                lvl++;
            }
            //密码中有其他字符加1
            if (pwdMsg.match(/^[0-9a-zA-Z]/)) {
                lvl++;
            }
            //密码小于6位减一
            if (pwdMsg.length <= 6) {
                lvl--;
            }
            return lvl;
        }
    </script>

页面内容：

<input type="text" id="txt" name="name" value="" />
    <table border="1" cellpadding="0" cellspacing="0" id="tb">
        <tr>
            <td>
                弱
            </td>
            <td>
                中
            </td>
            <td>
                强
            </td>
        </tr>
    </table>

简单的样式：

<style type="text/css">
        td
        {
            width: 100px;
            height: 25px;
            background-color: #E6E6E6;
            text-align: center;
        }
    </style>