Method setupElement_

src/service/fixed-layer.js:652–735

* This method records the potentially fixed or sticky element. One of a more * critical functions - it records all selectors that may apply "fixed" * or "sticky" to this element to check them later. * * @param {!Element} element * @param {string} selector * @param {string} position

(
    element,
    selector,
    position,
    opt_forceTransfer,
    opt_lightboxMode
  )

   * @private
   */
  setupElement_(
    element,
    selector,
    position,
    opt_forceTransfer,
    opt_lightboxMode
  ) {
    // Warn that pub-authored inline styles may be overridden by FixedLayer.
    if (!opt_forceTransfer) {
      this.warnAboutInlineStylesIfNecessary_(element);
    }

    // Ignore lightboxes because FixedLayer can interfere with their
    // opening/closing animations (#19149).
    if (isLightbox(element)) {
      return false;
    }
    const isLightboxDescendant = closest(element, isLightbox);
    if (!opt_lightboxMode && isLightboxDescendant) {
      return false;
    }

    const elements = this.elements_;

    // Avoid ancestor-descendant relationships in tracked elements to prevent
    // "double top-offset" (#22860).
    const removals = [];
    for (let i = 0; i < elements.length; i++) {
      const el = elements[i].element;
      if (el === element) {
        break;
      }
      // Early exit if element is a child of an already-tracked element...
      if (el.contains(element)) {
        return false;
      }
      // Remove the already-tracked element if it is a child of the new
      // element...
      if (element.contains(el)) {
        removals.push(el);
      }
    }
    for (let i = 0; i < removals.length; i++) {
      this.removeElement(removals[i]);
    }

    let fe = null;
    for (let i = 0; i < elements.length; i++) {
      const el = elements[i];
      if (el.element == element && el.position == position) {
        fe = el;
        break;
      }
    }
    const isFixed = position == 'fixed';
    if (fe) {
      if (!fe.selectors.includes(selector)) {
        // Already seen.