js 密码强弱的实现

页面代码：

<table>
        <tr><td><input type="text" id="txtPwd" /></td></tr>
        <tr><td>
            <table id="pwdLever">
                <tr>
                    <td>弱</td>
                    <td>中</td>
                    <td>强</td>
                </tr>
            </table>
        </td></tr>
    </table>

样式：

<style type="text/css">
        #pwdLever td
        {
           background-color:Gray;
           width:45px;
           text-align:center;
        }
    </style>

js代码：

<script type="text/javascript">
        window.onload = function () {
            var textInput = document.getElementById("txtPwd");
            //给密码输入框 注册键放开事件
            textInput.onkeyup = function () {
                var pwdValue = this.value;
                var num = pwdChange(pwdValue);
                var tds = document.getElementById("pwdLever").getElementsByTagName("td");
                //修改密码颜色
                if (num == 0 || num == 1) {
                    tds[0].style.backgroundColor = "red";
                    tds[1].style.backgroundColor = "gray";
                    tds[2].style.backgroundColor = "gray";
                }
                else if (num == 2) {
                    tds[0].style.backgroundColor = "red";
                    tds[1].style.backgroundColor = "red";
                    tds[2].style.backgroundColor = "gray";
                }
                else if (num == 3) {
                    tds[0].style.backgroundColor = "red";
                    tds[1].style.backgroundColor = "red";
                    tds[2].style.backgroundColor = "red";
                }
                else {
                    tds[0].style.backgroundColor = "gray";
                    tds[1].style.backgroundColor = "gray";
                    tds[2].style.backgroundColor = "gray";
                }
            }
        }
        function pwdChange(v) {
            var num = 0;
            var reg = /\d/; //如果有数字
            if (reg.test(v)) {
                num++;
            }
            reg = /[a-zA-Z]/; //如果有字母
            if (reg.test(v)) {
                num++;
            }
            reg = /[^0-9a-zA-Z]/; //如果有特殊字符
            if (reg.test(v)) {
                num++;
            }
            if (v.length < 6) { //如果密码小于6
                num--;
            }
            return num;
        }
    </script>