Function cancelLeavingNodes

packages/core/src/animation/utils.ts:178–227

(tNode: TNode, newElement: HTMLElement, newLView?: LView)

 *   `TNode`) from the same logical view being re-rendered into a new DOM parent.
 */
export function cancelLeavingNodes(tNode: TNode, newElement: HTMLElement, newLView?: LView): void {
  const nodes = leavingNodes.get(tNode);
  if (!nodes || nodes.length === 0) return;

  const newParent = newElement.parentNode;
  const prevSibling = newElement.previousSibling;
  const newDeclarationView = getDeclarationView(newLView);

  for (let i = nodes.length - 1; i >= 0; i--) {
    const {el: leavingEl, declarationView: leavingDeclarationView} = nodes[i];
    const leavingParent = leavingEl.parentNode;
    // Cancel if the leaving element is:
    // - The direct previousSibling of the new element. This is reliable
    //   because Angular inserts new elements at the same position (before
    //   the container anchor) where the leaving element was, making them
    //   always adjacent. Covers @if toggling and same-VCR toggling.
    // - The leaving element IS the new element. This happens when a node is moved
    //   (e.g., drag-and-drop reordering). We must cancel its pending leave animation
    //   and ensure it's not physically removed from the DOM by marking it as reused.
    if (leavingEl === newElement) {
      nodes.splice(i, 1);
      reusedNodes.add(leavingEl);
      leavingEl.dispatchEvent(new CustomEvent('animationend', {detail: {cancel: true}}));
    } else if (prevSibling && leavingEl === prevSibling) {
      nodes.splice(i, 1);
      leavingEl.dispatchEvent(new CustomEvent('animationend', {detail: {cancel: true}}));
      leavingEl.parentNode?.removeChild(leavingEl);
    } else if (leavingParent && newParent && leavingParent !== newParent) {
      // The leaving element is in a different DOM parent than the entering one.
      // This is ambiguous: it can be the same logical view re-rendered into a new
      // container (e.g. a dynamic component re-created in a fresh CDK overlay
      // pane), which must be de-duplicated by removing it immediately; or it can
      // be a *distinct* instance of the same template (accordions, exclusive-
      // expansion menus, master/detail nav) that merely shares this `TNode` and
      // is legitimately leaving in its own parent. Only force-remove when the
      // entering element belongs to the SAME declaration view as the leaving one
      // — i.e. a true re-render of the same logical view. Distinct instances are
      // left alone so their `animate.leave` runs to completion.
      const sameLogicalView =
        newDeclarationView === null ||
        leavingDeclarationView === null ||
        newDeclarationView === leavingDeclarationView;
      if (sameLogicalView) {
        nodes.splice(i, 1);
        leavingEl.dispatchEvent(new CustomEvent('animationend', {detail: {cancel: true}}));
        leavingEl.parentNode?.removeChild(leavingEl);
      }
    }
  }
}

/**
 * Tracks the nodes list of nodes that are leaving the DOM so we can cancel any leave animations