Promise pool is a small, dependency free, library to manage the concurrent resolution of any number of promises. It is particularly useful when the promises are not all available upfront.
const PromisePool = require("async-promise-pool");
// concurrency is the only option for PromisePool and enables you to
// choose how many promises will run at once
const pool = new PromisePool({ concurrency: 3 });
// elsewhere add functions to the pool that produce promises. We use
// functions here to prevent the promises from immediately executing.
pool.add(() => thingThatReturnsAPromise());
// you can await pool.all to ensure that all promises in the pool are
// resolved before continuing.
await pool.all();