How to use the shifty.Tweenable.now function in shifty

play (iterations = -1) {
    cancelLoop(this);

    if (this._playState === PAUSED) {
      // Move the playhead to the correct position in the timeline if resuming
      // from a pause
      this._loopTimestamp += Tweenable.now() - this._pausedAtTime;
    } else {
      this._loopTimestamp = Tweenable.now();
    }

    this._timesToIterate = iterations;
    this._playState = PLAYING;

    // Start the update loop
    tick(this);

    fireEvent(this, 'playStateChange');
    fireEvent(this, 'play');

    return this;
  }

play (iterations = -1) {
    cancelLoop(this);

    if (this._playState === PAUSED) {
      // Move the playhead to the correct position in the timeline if resuming
      // from a pause
      this._loopTimestamp += Tweenable.now() - this._pausedAtTime;
    } else {
      this._loopTimestamp = Tweenable.now();
    }

    this._timesToIterate = iterations;
    this._playState = PLAYING;

    // Start the update loop
    tick(this);

    fireEvent(this, 'playStateChange');
    fireEvent(this, 'play');

    return this;
  }

pause () {
    if (this._playState === PAUSED) {
      return this;
    }

    this._playState = PAUSED;
    cancelLoop(this);
    this._pausedAtTime = Tweenable.now();

    fireEvent(this, 'playStateChange');
    fireEvent(this, 'pause');

    return this;
  }

export const calculateTimeSinceStart = rekapi =>
  Tweenable.now() - rekapi._loopTimestamp;

playFrom (millisecond, iterations) {
    this.play(iterations);
    this._loopTimestamp = Tweenable.now() - millisecond;

    this._actors.forEach(
      actor => actor._resetFnKeyframesFromMillisecond(millisecond)
    );

    return this;
  }