Throttle the parallelism of an asynchronous (promise returning) function / functions

Usage no npm install needed!

<script type="module">
  import throat from '';



Throttle the parallelism of an asynchronous, promise returning, function / functions. This has special utility when you set the concurrency to 1. That way you get a mutually exclusive lock.

Professionally supported throat is now available

Build Status Coveralls github branch Rolling Versions NPM version


npm install throat



This returns a function that acts a bit like a lock (exactly as a lock if concurrency is 1).

Example, only 2 of the following functions will execute at any one time:

const throat = require('throat')(2);

const resA = throat(async () => { /* async stuff... */ });
const resB = throat(async () => { /* async stuff... */ });
const resC = throat(async () => { /* async stuff... */ });
const resD = throat(async () => { /* async stuff... */ });
const resE = throat(async () => { /* async stuff... */ });

throat(concurrency, worker)

This returns a function that is an exact copy of worker except that it will only execute up to concurrency times in parallel before further requests are queued:

const throat = require('throat');

const input = ['fileA.txt', 'fileB.txt', 'fileC.txt', 'fileD.txt'];
const data = Promise.all(, (fileName) => readFile(fileName)))

Only 2 files will be read at a time, sometimes limiting parallelism in this way can improve scalability.

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