Function trackLeavingNodes

packages/core/src/animation/utils.ts:236–251

(tNode: TNode, el: HTMLElement, lView?: LView)

 * duplicates from showing up on screen mid-animation.
 */
export function trackLeavingNodes(tNode: TNode, el: HTMLElement, lView?: LView): void {
  // We need to track this tNode's element just to be sure we don't add
  // a new RNode for this TNode while this one is still animating away.
  // once the animation is complete, we remove this reference.
  // The declaration view is recorded so `cancelLeavingNodes` can tell apart two
  // separate instances of the same template from the same view re-rendered.
  const declarationView = getDeclarationView(lView);
  const nodes = leavingNodes.get(tNode);
  if (nodes) {
    if (!nodes.some((node) => node.el === el)) {
      nodes.push({el, declarationView});
    }
  } else {
    leavingNodes.set(tNode, [{el, declarationView}]);
  }
}

/**
 * Retrieves the list of specified enter animations from the lView