_observerCallback()

in _/js/bootstrap.esm.js [3877:3908]

• 28 lines of code
• 9 McCabe index (conditional complexity)

  _observerCallback(entries) {
    const targetElement = entry => this._targetLinks.get(`#${entry.target.id}`);
    const activate = entry => {
      this._previousScrollData.visibleEntryTop = entry.target.offsetTop;
      this._process(targetElement(entry));
    };
    const parentScrollTop = (this._rootElement || document.documentElement).scrollTop;
    const userScrollsDown = parentScrollTop >= this._previousScrollData.parentScrollTop;
    this._previousScrollData.parentScrollTop = parentScrollTop;
    for (const entry of entries) {
      if (!entry.isIntersecting) {
        this._activeTarget = null;
        this._clearActiveClass(targetElement(entry));
        continue;
      }
      const entryIsLowerThanPrevious = entry.target.offsetTop >= this._previousScrollData.visibleEntryTop;
      // if we are scrolling down, pick the bigger offsetTop
      if (userScrollsDown && entryIsLowerThanPrevious) {
        activate(entry);
        // if parent isn't scrolled, let's keep the first visible item, breaking the iteration
        if (!parentScrollTop) {
          return;
        }
        continue;
      }

      // if we are scrolling up, pick the smallest offsetTop
      if (!userScrollsDown && !entryIsLowerThanPrevious) {
        activate(entry);
      }
    }
  }