A module which returns an observable for a key. It streams `pressed` and `released` observations. Also has a getter for the pressed state of a key.

observe-key.js

import Observable from 'zen-observable';

export default function observeKey(key) {
  let pressed = false;

  const observable = new Observable(observer => {
    function downHandler(e) {
      if (e.key === key && !pressed) {
        pressed = true;
        observer.next('pressed');
      }
    }

    function upHandler(e) {
      if (e.key === key && pressed) {
        pressed = false;
        observer.next('released');
      }
    }

    window.addEventListener('keydown', downHandler, false);
    window.addEventListener('keyup', upHandler, false);

    return () => {
      window.removeEventListener('keydown', downHandler);
      window.removeEventListener('keyup', upHandler);
    };
  });

  Object.defineProperty(observable, 'pressed', {
    get() {
      return pressed;
    }
  });

  return observable;
}