// IDs we want to fetch
const userIds = [1, 2, 3, 4, 5];
// Final results array
const results = [];
// Function to fetch a single user
async function fetchUser(id) {
  const response = await fetch(
    `https://jsonplaceholder.typicode.com/users/${id}`
  );
  return response.json();
}
// Promise Pool
async function promisePool(ids, limit) {
  let index = 0;
  async function worker() {
    while (index < ids.length) {
      // Take next available ID
      const currentIndex = index++;
      // Current ID
      const id = ids[currentIndex];
      console.log(`Fetching User ${id}`);
      // Wait for API response
      const user = await fetchUser(id);
      // Store result at correct position
      results[currentIndex] = user;
      console.log(`Completed User ${id}`);
    }
  }
  // Create workers
  const workers = Array(limit)
    .fill(null)
    .map(() => worker());
  // Wait for all workers
  await Promise.all(workers);
  return results;
}
// Run with max 2 concurrent requests
promisePool(userIds, 2)
  .then(data => {
    console.log("Final Results");
    console.log(data);
  })
  .catch(console.error);