Nested.js

const DataLoader = require("dataloader");

const users = new Map([
  [
    1,
    {
      id: 1,
      name: "Tom",
    },
  ],
  [
    2,
    {
      id: 2,
      name: "Peter",
    },
  ],
  [
    3,
    {
      id: 3,
      name: "Mary",
    },
  ],
  [
    4,
    {
      id: 4,
      name: "John",
    },
  ],
  [
    5,
    {
      id: 5,
      name: "Tommy",
    },
  ],
  [
    6,
    {
      id: 6,
      name: "Johnny",
    },
  ],
  [
    7,
    {
      id: 7,
      name: "Betty",
    },
  ],
  [
    8,
    {
      id: 8,
      name: "Alex",
    },
  ],
  [
    9,
    {
      id: 9,
      name: "Gary",
    },
  ],
]);

const replies = [
  {
    user_id: 1,
    content: "dummy 1",
    replies: [
      {
        user_id: 2,
        content: "dummy 2",
        replies: [],
      },
      {
        user_id: 1,
        content: "dummy 3",
        replies: [
          {
            user_id: 5,
            content: "dummy 14",
            replies: [
              {
                user_id: 8,
                content: "dummy 15",
                replies: [],
              },
              {
                user_id: 9,
                content: "dummy 16",
                replies: [],
              },
            ],
          },
        ],
      },
      {
        user_id: 3,
        content: "dummy 4",
        replies: [
          {
            user_id: 2,
            content: "dummy 5",
            replies: [],
          },
        ],
      },
    ],
  },
  {
    user_id: 2,
    content: "dummy 6",
    replies: [
      {
        user_id: 1,
        content: "dummy 7",
        replies: [
          {
            user_id: 6,
            content: "dummy 13",
            replies: [],
          },
        ],
      },
      {
        user_id: 3,
        content: "dummy 8",
        replies: [],
      },
      {
        user_id: 1,
        content: "dummy 9",
        replies: [
          {
            user_id: 2,
            content: "dummy 10",
            replies: [],
          },
          {
            user_id: 7,
            content: "dummy 11",
            replies: [],
          },
        ],
      },
      {
        user_id: 4,
        content: "dummy 12",
        replies: [],
      },
    ],
  },
];

const userLoader = new DataLoader(async (ids) => {
  console.log("user loader has been called with", ids);
  return ids.map((id) => users.get(id));
});

// batch all nested
const repliesAggregatorNoAwait = async (replies) =>
  Promise.all(
    replies.map(async ({ user_id, replies: nestedReplies, content }) => ({
      user: userLoader.load(user_id),
      content,
      replies: repliesAggregatorNoAwait(nestedReplies),
    }))
  );

const repliesResolver = async (repliesPromises) =>
  Promise.all(
    (await repliesPromises).map(
      async ({ user, replies: nestedRepliesPromises, content }) => ({
        user: await user,
        content,
        replies: await repliesResolver(nestedRepliesPromises),
      })
    )
  );

(async () => {
  /**
   * Await all .load outside the recursive aggregator can perform optimized batching
   *
   */
  const repliesPromises = repliesAggregatorNoAwait(replies);
  // user loader has been called with [ 1, 2, 5, 8, 9, 3, 6, 7, 4 ]
  const values = await repliesResolver(repliesPromises);

  console.log("values:", JSON.stringify(values, null, 2));
})();