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>