JS實現根據密碼長度 顯示安全條

//根據密碼長度顯示安全條


                <ul class="clear">
                <li>密　　碼：</li>
                <li> <input type="password" id="pwd" name="pwd" class="in" onKeyUp=pwStrength(this.value) onBlur=pw_y("pwd","pwd1")></li>
                <li><em class="red">*</em></li>
                <li class="i2 grey"><table border="0" bordercolor="#cccccc" style='display:marker'>
                <tr align="center">
                    <td  id="strength_L"  bgcolor="#eeeeee">弱</td>
                    <td  id="strength_M" bgcolor="#eeeeee">中</td>
                    <td id="strength_H" bgcolor="#eeeeee">強</td>
                <td align="left" >
                  <label id="pwd1">使用數字，字母，下劃線，長度在 6 - 20 個字符之間</label></td>
                    </tr>
                </table>                 
                </li>
                </ul>


function pwStrength(pwd){
    O_color="#eeeeee";
    L_color="#FF0000";
    M_color="#FF9900";
    H_color="#33CC00";
    if (pwd==null||pwd==''){
        Lcolor=Mcolor=Hcolor=O_color;
    }else{
        S_level=checkStrong(pwd);
        switch(S_level) {
            case 0:
                Lcolor=Mcolor=Hcolor=O_color;
            case 1:
                Lcolor=L_color;
                Mcolor=Hcolor=O_color;
                break;
            case 2:
                Lcolor=Mcolor=M_color;
                Hcolor=O_color;
                break;
            default:
                Lcolor=Mcolor=Hcolor=H_color;
            }
    }
    document.getElementById("strength_L").style.background=Lcolor;
    document.getElementById("strength_M").style.background=Mcolor;
    document.getElementById("strength_H").style.background=Hcolor;
    return;
} </pre>