_observerCallback()

in applications/clouddemo/net4/CloudDemo.Mvc/Scripts/bootstrap.esm.js [4529:4568]

• 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);
      }
    }
  }