example.js

const memTester = (() => {
  const api = {
    _timer: null,
    start() {
      if (api._timer != null) {
        api.end();
      }
      let back = true;
      api._timer = setInterval(() => {
        if (back) {
          window.history.back();
          back = false;
        } else {
          window.history.forward();
          back = true;
        }
      }, 100)
    },
    end() {
      clearInterval(api._timer);
      api._timer = null;
    }
  }
  return api
})();