I think the description could be expanded to answer:

• Are the numbers always integers or can then be any number?
• If there a min/max for the "digits"?

Also, I imagine that this will require me to store some global state which I need to clear each time my function is called with null. I agree with @arnedag that it would probably be cleaner if you passed the guess function as the parameter, then returned indications on a bad guess, returned true on success, or threw an error if we made too many guesses.

Here is an example of what that might look like:

function breakCode(makeGuess) {
  var guess = [x, y, z];
  var indications;
  
  while (true !== (indications = makeGuess(guess))) {
    // use indications to update guess
  }
}