docs: function _tick() {
      var config = this._config;
      var now = Date.now();
      var dt = now - this._before;
  
      if (!this._started) {
        // The ticker has been stopped
        return;
      }
  
      if (config.async) {
        config.task(this._tock, dt);
      } else {
        config.task(dt);
        this._tock();
      }
    }