如何限制textarea长度

Question

中文为2个字节
function limitLength(obj, length) { var desc = obj.value;
desc = desc.replace(/[\u4e00-\u9fa5]/g,"   ");

        if(desc.length >= length) { 
         alert("");//这里怎么用substr呢？注意前提“中文为2个字节”
        } 
}
  <textarea name="blogdesc" cols="50" rows="5" onkeyup="limitLength(this,200)">恍恍惚惚恍恍惚惚恍恍惚惚和</textarea>

Answer 1

<script>
function limitLength(obj, length) { 
    var desc = obj.value; 
    desc = desc.replace(/[\u4e00-\u9fa5]/g,"  ");     if(desc.length >= length) { 
        alert(substr(obj.value,length)); 
    } 
} 
function substr(str,length){
    var l=0,i=0;
    while(l<length){
        l+=1;
        if(str.substring(i,1).match(/[\u4e00-\u9fa5]/))l+=1;
        i+=1;
    }
    return str.substring(0,i-1);
}
</script>  <textarea name="blogdesc" cols="50" rows="5" onkeyup="limitLength(this,20)">恍恍惚惚恍恍惚惚恍恍惚惚和 </textarea>

Answer 2

length不正确我前面有
desc = desc.replace(/[\u4e00-\u9fa5]/g,"  "); 

Answer 3

<script>
function limitLength(obj, length) { 
    var desc = obj.value; 
    desc = desc.replace(/[\u4e00-\u9fa5]/g,"  ");     if(desc.length >= length) { 
        alert(substr(obj.value,length)); 
    } 
} 
function substr(str,length){
    var l=0,i=0;
    while(l<length){
        l+=1;
        if(str.substring(i,1).match(/[\u4e00-\u9fa5]/))l+=2;//一个中文是相当于3个英文
        i+=1;
    }
    return str.substring(0,i-1);
}
</script>  <textarea name="blogdesc" cols="50" rows="5" onkeyup="limitLength(this,20)">恍恍惚惚恍恍惚惚恍恍惚惚和 </textarea>

Answer 4

<script> 
function limitLength(obj, length) { 
    var desc = obj.value;  
    alert(substr(obj.value,length)); 
} 
function substr(str,length){ 
    var l=0,i=0; 
    while(l <length && i<str.length){ 
        l+=1; 
        if(str.substring(i,i+1).match(/[\u4e00-\u9fa5]/))l+=2;//一个中文是相当于3个英文 
        i+=1; 
    } 
    return str.substring(0,i); 
} 
</script>   <textarea name="blogdesc" cols="50" rows="5" onkeyup="limitLength(this,20)">恍恍惚惚恍恍惚惚恍恍惚惚和 </textarea>