Function navigateBetween

packages/core/src/hydration/node_lookup_utils.ts:297–321

(start: Node, finish: Node)

 * and `.nextSibling` operations.
 */
export function navigateBetween(start: Node, finish: Node): NodeNavigationStep[] | null {
  if (start === finish) {
    return [];
  } else if (start.parentElement == null || finish.parentElement == null) {
    return null;
  } else if (start.parentElement === finish.parentElement) {
    return navigateBetweenSiblings(start, finish);
  } else {
    // `finish` is a child of its parent, so the parent will always have a child.
    const parent = finish.parentElement!;

    const parentPath = navigateBetween(start, parent);
    const childPath = navigateBetween(parent.firstChild!, finish);
    if (!parentPath || !childPath) return null;

    return [
      // First navigate to `finish`'s parent
      ...parentPath,
      // Then to its first child.
      NODE_NAVIGATION_STEP_FIRST_CHILD,
      // And finally from that node to `finish` (maybe a no-op if we're already there).
      ...childPath,
    ];
  }
}

/**
 * Calculates a path between 2 sibling nodes (generates a number of `NextSibling` navigations).