keyCode values for numeric keypad?

The keycodes are different. Keypad 0-9 is Keycode 96 to 105

Your if statement should be:

if ((e.keyCode >= 48 && e.keyCode <= 57) || (e.keyCode >= 96 && e.keyCode <= 105)) { 
  // 0-9 only
}

Here's a reference guide for keycodes

---

-- UPDATE --

This is an old answer and keyCode has been deprecated. There are now alternative methods to achieve this, such as using key:

if ((e.key >= 48 && e.key <= 57) || (e.key >= 96 && e.key <= 105)) { 
  // 0-9 only
}

Here's an output tester for event.key, thanks to @Danziger for the link.