title: Differentiate which keyboard (not key) was pressed in Javascript
body: <p>I have 2 USB keyboards plugged in. How can I determine which one was pressed?</p>
  
  <p>I can use <code>keyCode</code> for my events but I don't see something about getting a read on which keyboard was used.</p>
  
  <p>Gamepads, on the other hand, have an index for which gamepad in the navigator's list was used. I'm looking for something like that.</p>