This Gist demonstrates how to keep control a maximum of concurrent promises using standard NodeJs Promises.

many-promises-with-max-concurrent-limit.js.js

const CONCURRENT_LIMIT = 3

const workUnits = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j']

/** Returns a Promise that resolves after `milliseconds` */
const sleep = (milliseconds = 1) => new Promise((resolve) => setTimeout(resolve, milliseconds))

/** Placeholder for any business-related async function */
const worker = async (id) => {
  console.log(`working on ${id}`)
  await sleep( 100 * Math.random() )
  console.log(`${id} is completed`)
}

const poc = async() => {
  let semaphore = 0
  for(const id of workUnits) {
    // wait for an available "slot" to run the worker
    while(semaphore >= CONCURRENT_LIMIT) { await sleep() }
    semaphore++
    void worker(id).finally(() => semaphore--)
  }

  // wait all pending promises
  while(semaphore) { await sleep() }
}

poc()

This code emerged from an atual problem, when I needed to use an asynchronous API a number of times, but this API had a limit of concurrent calls. Since the expected total number of API calls would be higher of the API concurrent calls limit, using Promise.allSettled() was not an option. On the other side, using wait on each call would make all the waiting times cumulative, and that was not ideal.

This code keeps at most CONCURRENT_LIMIT pending Promises at a time and waits then before making more asynchronous calls, until all the workUnits are processed.