How to use the @lumino/algorithm.ArrayExt.findLastIndex function in @lumino/algorithm

private _activatePreviousItem(): void {
    // Bail if there are no search results.
    if (!this._results || this._results.length === 0) {
      return;
    }

    // Find the previous enabled item index.
    let ai = this._activeIndex;
    let n = this._results.length;
    let start = ai <= 0 ? n - 1 : ai - 1;
    let stop = start === n - 1 ? 0 : start + 1;
    this._activeIndex = ArrayExt.findLastIndex(
      this._results, Private.canActivate, start, stop
    );

    // Schedule an update of the items.
    this.update();
  }

activatePreviousItem(): void {
    let n = this._items.length;
    let ai = this._activeIndex;
    let start = ai <= 0 ? n - 1 : ai - 1;
    let stop = start === n - 1 ? 0 : start + 1;
    this.activeIndex = ArrayExt.findLastIndex(
      this._items, Private.canActivate, start, stop
    );
  }