Caching.js

const DataLoader = require("dataloader");

const users = new Map([
  [1, { id: 1, name: "Tom" }],
  [2, { id: 2, name: "John" }],
  [3, { id: 3, name: "Ann" }],
  [4, { id: 4, name: "Peter" }],
  [5, { id: 5, name: "May" }],
]);

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

const loader = new DataLoader(batchLoadFn);

Promise.all([
  // Loaded 3 authors from the original comment list
  loader.load(1),
  loader.load(2),
  loader.load(3),
])
  .then((results) => {
    // batchLoadFn has only been called once here
    console.log(results);
    // [
    //   { id: 1, name: 'Tom' },
    //   { id: 2, name: 'John' },
    //   { id: 3, name: 'Ann' }
    // ]
  })
  .then(() => {
    return Promise.all([
      // Load additional authors who were loaded before when open sub-comments
      loader.load(1),
      loader.load(2),
    ]);
  })
  .then((results) => {
    // Resolve directly without calling batchLoadFn
    console.log(results);
    // [
    //   { id: 1, name: 'Tom' },
    //   { id: 2, name: 'John' }
    // ]
  });