function isNum(from) {
   var charStr;
   var counter = 0;
   var i = 0;
   var re = /[0-9]/;
   for (i; i < from.value.length ;  i++) {
      charStr = from.value.substring(i, i+1);
      if (re.test(charStr))
              counter ++;
   }
   if (counter != from.value.length) {
     return false;
   }
   return true;
}