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<script type="text/javascript">
        //CharMode函数 
        //测试某个字符是属于哪一类. 
        function CharMode(iN){ 
            if (iN>=48 && iN <=57) //数字 
            return 1; 
            if (iN>=65 && iN <=90) //大写字母 
            return 2; 
            if (iN>=97 && iN <=122) //小写 
            return 4; 
            else 
            return 8; //特殊字符 
        } 

        //bitTotal函数 
        //计算出当前密码当中一共有多少种模式 
        function bitTotal(num){ 
            modes=0; 
            for (i=0;i<4;i++){ 
            if (num & 1) modes++; 
            num>>>=1; 
            } 
            return modes; 
        } 

        //checkStrong函数 
        //返回密码的强度级别 

        function checkStrong(sPW){ 
            if (sPW.length<=4) 
            return 0; //密码太短 
            Modes=0; 
            for (i=0;i<sPW.length;i++){ 
            //测试每一个字符的类别并统计一共有多少种模式. 
            Modes|=CharMode(sPW.charCodeAt(i)); 
        } 

        return bitTotal(Modes); 

        } 

        //pwStrength函数 
        //当用户放开键盘或密码输入框失去焦点时,根据不同的级别显示不同的颜色 

        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; 
        }
 </script>
 <form name=form1 action="" > 
输入密码:<input type=password size=10 onKeyUp=pwStrength(this.value) onBlur=pwStrength(this.value)> 
<br>密码强度: 
<table width="217" border="1" cellspacing="0" cellpadding="1" bordercolor="#cccccc" height="23" style='display:inline'> 
<tr align="center" bgcolor="#eeeeee"> 
<td width="33%" id="strength_L">弱</td> 
<td width="33%" id="strength_M">中</td> 
<td width="33%" id="strength_H">强</td> 
</tr> 
</table> 
</form>
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??转自：http://www.cnblogs.com/zyh-nhy/archive/2007/05/10/741427.html

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