How to allow numbers, backspace, delete, left and right arrow keys in the html text?

Question

I am using following javascript code which I think should only allow numbers, backspace, delet, left arrow and right arrow keys in textbox, but it is also allowing alphabets. I

Answer 1

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