CHUNKS.get.js

async function findOneMongoDB(query) {
  /* implemented somewhere */
}

async function get(query) {
  let doc = await findOneMongoDB(query);
  // return doc at once if it is not splitted
  if (!doc._splitted) return doc;

  const { _id, type } = doc;
  const values = [];

  while (doc._next) {
    // our doc and its chunks is a linked list
    // empty[] -> values[] -> values[]
    // id of the next chunk is in `_next` property
    doc = await get({ _id: doc._next });
    // here we will use for..of statement
    // read about benefits https://medium.com/@baranovxyz/499269312eaf
    for (const value of doc.values) {
      values.push(value);
    }
  }

  return { _id, type, values };
}