Centralized fetcher function that caches the response.

centralFetcher.js

const _sessionStore = {};
const sessionStore = {
  getItem: (id) => _sessionStore[id] || null,
  setItem: (id, value) => _sessionStore[id] = value,
  clear: () => _sessionStore = {},
}

/**
 * 
 * @template T
 * @param {number} ms 
 * @param {T} value 
 * @returns {Promise<T>}
 */
const sleep = (ms, value) => new Promise(resolve => setTimeout(resolve, ms, value));

const LOADING_TAG = '%%LOADING%%';

/**
 * @async
 * @template T
 * @param {string} id 
 * @param {() => Promise<T>} fn 
 * @param {{ defaultTimeout: number }} config 
 * @returns {T}
 */
async function centralFetcher(id, fn, config = { defaultTimeout: 100, defaultStorage: sessionStore }) {
  const localValue = config.defaultStorage.getItem(id);
  if (localValue === LOADING_TAG) {
    await sleep(config.defaultTimeout);
    return centralFetcher(id, fn);
  }
  if (localValue === null) {
    config.defaultStorage.setItem(id, LOADING_TAG);
    const value = await fn();
    config.defaultStorage.setItem(id, value);
    return value;
  }
  return localValue;
}

run.js

async function run() {
  try {
    const values = await Promise.all([
      centralFetcher('a', () => sleep(100, 1)),
      centralFetcher('b', () => sleep(200, 2)),
      centralFetcher('a', () => sleep(300, 3)),
      centralFetcher('b', () => sleep(500, 4)),
//       centralFetcher('c', () => reject(500, Error('Ha ocurrido un error'))),
    ]);
    console.log('values', values);
  } catch (err) {
    console.error("Run err", err.message);
  }
}

run();