EventListener

• isNumberKey()
• Enter Key : e.keyCode == 13

isNumberKey

   onkeypress = "return isNumberKey(event);"

   function isNumberKey(evt){
      var chartCode = (evt.which)?evt.which:event.keyCode;
      if(charCode > 31 && (chartCode < 48 || charCode > 57))
         return false;
      return true;
   }