限制字条内容的长度

最多允许<input name='total',type=''text', disabled class='',
       id='total', value='200', size='4'>
个字节，已用字节：&nbsp;
<input name='used',type=''text', disabled class='',
       id='used',  size='4'>
剩余字节：
<input name='remain',type=''text', disabled class='',
       id='remain',  size='4'>
<textarea name='content' id=='content' rows='6' cols='9'
class='',onkeydown='CountStrByte(this,this.form.total,this.form.used,
this.form.remain);',onkeyup='CountStrByte(this,this.form.total,this.form.used,
this.form.remain);'></textarea>

<script type='javascript'  >

function CountStrByte(info,Total,Used,Remain){
  var ByteCount=0;
  var StrValue=info.value;
  var StrLength=info.value.length;
  var MaxValue=Total.vaule;
  if(LastCount !=StrLength){
        

    for(i=0;i<StrLength;i++){
        ByteCount=(StrValue.charCodeAt(i)<=256)?ByteCount+1:ByteCount+2;
        if(ByteCount>MaxValue){
            info.value=StrValue.substring(0,i);
            document.getElementById('pContext').innerHTML=info.value;
            alert();
            ByteCount=MaxValue;
            break; 
          }
         }
       Used.value=ByteCount;
       Remain.value=MaxValue-ByteCount;
       document.getElementById('pContext').innerHTML=StrValue;
      }
}
</script>