Create an in memory cache with ttl. Fetch and serve data from this cache

fetchAndCache.js

class InMemoryCache {
  constructor() {
    this._cache = {};
    this._timeouts = {};
  }

  set(key, value, time) {
    if (this._timeouts[key]) {
      clearTimeout(this._timeouts[key]);
      delete this._timeouts[key];
    }

    this._cache[key] = value;

    if (!isNaN(time)) {
      this._timeouts[key] = setTimeout(() => this.del(key), time);
    }
  }

  get(key) {
    if (typeof key === 'undefined') {
      return this._cache;
    }

    return this._cache.hasOwnProperty(key) ? this._cache[key] : null;
  }

  del(key) {
    clearTimeout(this._timeouts[key]);
    delete this._timeouts[key];

    if (!(key in this._cache)) {
      return false;
    }

    delete this._cache[key];
    return true;
  }
}

const myCache = new InMemoryCache();

function getCompanyNameFromCache(userName) {
  const companyName = myCache.get(userName);

  // return companyName ? companyName : null;
   return companyName ? `${companyName} :from cache` : null;
}

function setCompanyNameInCache(userName, companyName) {
  // time in ms
  myCache.set(userName, companyName, 2000);
}

async function getAllUsersFromAPI() {
  try {
    const res = await fetch("https://3dc15088-204f-4ec5-90eb-af7cd840d7ec.mock.pstmn.io/users");
    const users = await res.json();

    return users;
  } catch (err) {
    console.log(err.message); // can be console.error
  }
}

async function getUserCompanyName(userName) {
  const companyNameFromCache = getCompanyNameFromCache(userName);

  if (companyNameFromCache) {
    return companyNameFromCache;
  }

  const users = await getAllUsersFromAPI();

  if (!users) {
    return null;
  }

  const user = users.find((user) => user.username === userName);
  const companyName = user?.company?.name;

  setCompanyNameInCache(userName, companyName);

  return companyName;
}

async function fetchAndCache() {
  const userName1 = "Moriah.Stanton";
  const userName2 = "Maxime_Nienow";

  let companyName = await getUserCompanyName(userName1); // from API
  console.log(companyName);
  companyName = await getUserCompanyName(userName1); // from cache
  console.log(companyName);

  // wait for 5 seconds
  await new Promise((resolve) => setTimeout(resolve, 5000));

  companyName = await getUserCompanyName(userName1); // from API
  console.log(companyName);
  companyName = await getUserCompanyName(userName2); // from API
  console.log(companyName);
}

fetchAndCache();