Batching.js

const DataLoader = require("dataloader");

const stories = new Map([
  [1, { id: 1, title: "story 1" }],
  [2, { id: 2, title: "story 2" }],
  [3, { id: 3, title: "story 3" }],
  [4, { id: 4, title: "story 4" }],
  [5, { id: 5, title: "story 5" }],
]);

const batchLoadFn = async (ids) => ids.map((id) => stories.get(id));

const loader = new DataLoader(batchLoadFn);

Promise.all([
  loader.load(1),
  loader.load(2),
  loader.load(3),
  loader.load(1),
  loader.load(4),
]).then((results) => {
  // batchLoadFn has only been called once
  console.log(results);
  // [
  //   { id: 1, title: 'story 1' },
  //   { id: 2, title: 'story 2' },
  //   { id: 3, title: 'story 3' },
  //   { id: 1, title: 'story 1' },
  //   { id: 4, title: 'story 4' }
  // ]
});