Function walk

packages/markmap-common/src/util.ts:18–23

(item: T, parent?: T)

  callback: (item: T, next: () => U[] | undefined, parent?: T) => U,
): U {
  const walk = (item: T, parent?: T): U =>
    callback(
      item,
      () => item.children?.map((child: T) => walk(child, item)),
      parent,
    );
  return walk(tree);
}