Method tickLayoutShiftScore_

src/service/performance-impl.js:592–621

* Tick the layout shift metric, following the latest CWV standard. This uses * a 5s maximum window with a 1s gap between events to define a "session". * We report the maximum session value over the lifetime of the page as the CLS. * * @param {!LayoutShift} entry

(entry)

   * @param {!LayoutShift} entry
   */
  tickLayoutShiftScore_(entry) {
    if (!this.ampdoc_) {
      return;
    }

    if (this.isVisibilityHidden_()) {
      return;
    }

    const entries = this.layoutShiftEntries_;
    if (entries.length > 0) {
      const first = entries[0];
      const last = entries[entries.length - 1];
      if (
        entry.startTime - last.startTime < CLS_SESSION_GAP &&
        entry.startTime - first.startTime < CLS_SESSION_MAX
      ) {
        // This entry continues the current CLS window.
        entries.push(entry);
        return;
      }
      // This entry is the start of a new CLS window, but we haven't flushed the old value yet.
      this.flushLayoutShiftScore_();
    }
    entries.push(entry);
    // Ensure we report the CLS when the session closes. We're not guaranteed
    // to get more LayoutShift entries, so we need some setTimeout magic to
    // ensure it happens.
    this.debouncedFlushLayoutShiftScore_();
  }

  /**
   * Records the normalized CLS score, following the latest CWV standard.