How to use the boring-router.getActiveHistoryEntryIndex function in boring-router

private restoreActive(): void {
    let expectedActiveIndex = getActiveHistoryEntryIndex(this.snapshot);
    let trackedActiveIndex = getActiveHistoryEntryIndex(this.tracked);

    if (trackedActiveIndex < expectedActiveIndex) {
      history.forward();
    } else if (trackedActiveIndex > expectedActiveIndex) {
      history.back();
    } else {
      this.completeRestoration();
    }
  }

private restoreEntries(): void {
    let expected = this.snapshot;
    let tracked = this.tracked;

    let {entries: expectedEntries} = expected;
    let {entries: trackedEntries} = tracked;

    let lastExpectedIndex = expectedEntries.length - 1;
    let lastTrackedIndex = trackedEntries.length - 1;

    let trackedActiveIndex = getActiveHistoryEntryIndex(tracked);

    let minLength = Math.min(expectedEntries.length, trackedEntries.length);

    let firstMismatchedIndex = 0;

    for (
      firstMismatchedIndex;
      firstMismatchedIndex < minLength;
      firstMismatchedIndex++
    ) {
      let expectedEntry = expectedEntries[firstMismatchedIndex];
      let trackedEntry = trackedEntries[firstMismatchedIndex];

      if (!isHistoryEntryEqual(expectedEntry, trackedEntry)) {
        break;
      }

private pushEntry({
    id,
    ref,
    data,
  }: BrowserHistoryEntry): BrowserHistorySnapshot {
    let tracked = this.tracked;

    let {entries} = tracked;

    let activeIndex = getActiveHistoryEntryIndex(tracked);

    let snapshot: BrowserHistorySnapshot = {
      entries: [...entries.slice(0, activeIndex + 1), {id, ref, data}],
      active: id,
    };

    this.tracked = snapshot;

    let href = this.getHRefByRef(ref);

    try {
      history.pushState({id, data}, '', href);
    } catch (error) {
      history.pushState({id}, '', href);
    }