isForward = () => {
    if (timer.direction === "normal") {
      return true;
    } else if (timer.direction === "reverse") {
      return false;
    } else if (timer.direction === "alternate") {
      return timer.iterationStartCount % 2 === 1;
    } else if (timer.direction === "alternate-reverse") {
      return timer.iterationStartCount % 2 === 0;
    }
  }
make a timer for timeline animation

@param {*} opt