js判断字符长度

   function getByteLen(){
    var val=document.getElementById("txtPrizeNote").value;
    var re = new RegExp("[\\u4e00-\\u9fa5]","");// 中文
        var len = 0;
    for(var i=val.length;i>0;i--){     
     var singleVal = val.substring(i,i-1);// 单个
     if(re.test(singleVal))
      len+=2;
     else
      len++;
     var tempVal = val.substring(0,i-1);// 剩余
     //alert(tempVal+" = =  "+singleVal);
    }
    alert(len);
   }