javascript 截取中文长度

  //按单字节计算字符串的长度
function getStrLen(str){
var len = 0;
var cnstrCount = 0;
for(var i = 0 ; i < str.length ; i++){
  if(str.charCodeAt(i)>255)
   cnstrCount = cnstrCount + 1 ;
}
len = str.length + cnstrCount;
return len;
}

<script language="JavaScript" type="text/JavaScript">
document.write(getNewsTitle('filename',24));
</script>