Help with my mouse orbit script (movement)?

Hi
If you've ever played Dead Space than you'll understand what I want. I want the Y axis (rotation) of my FPSController to lerp to the same Y axis as the MainCamera when you either hold the Horizontal, Vertical, or Aim input. How you'd I do this? If you need an example then here's some Dead Space Gameplay.

P.S. I prefer JavaScript but anything works. Thanks!!!