Javascript String charLength()

String.prototype.charLength = function() {
 var len = 0;//from  w  w w .  j  a  v  a  2 s .  com
 for (var i = 0; i < this.length; i++) {
  var c = this.charCodeAt(i);
  if ((c >= 0x0001 && c <= 0x007e) || (0xff60 <= c && c <= 0xff9f))
   len += 1;
  else
   len += 2;
 }
 return len;
};