handleEvent(mapBrowserEvent) {
    let stopEvent = false;
    if (
      mapBrowserEvent.type == EventType.KEYDOWN ||
      mapBrowserEvent.type == EventType.KEYPRESS
    ) {
      const keyEvent = /** @type {KeyboardEvent} */ (
        mapBrowserEvent.originalEvent
      );
      const key = keyEvent.key;
      if (this.condition_(mapBrowserEvent) && (key === '+' || key === '-')) {
        const map = mapBrowserEvent.map;
        const delta = key === '+' ? this.delta_ : -this.delta_;
        const view = map.getView();
        zoomByDelta(view, delta, undefined, this.duration_);
        keyEvent.preventDefault();
        stopEvent = true;
      }
    }
    return !stopEvent;
  }
Handles the {@link module:ol/MapBrowserEvent~MapBrowserEvent map browser event} if it was a
`KeyEvent`, and decides whether to zoom in or out (depending on whether the
key pressed was '+' or '-').
@param {import("../MapBrowserEvent.js").default} mapBrowserEvent Map browser event.
@return {boolean} `false` to stop event propagation.
@override