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asynchronous function queue with adjustable concurrency

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Asynchronous function queue with adjustable concurrency.

Async is a big library offering various approaches to dealing with asynchrony; queue is a small library offering a single, flexible abstraction.

This module exports a class Queue that implements most of the Array API. Pass async functions (ones that accept a callback) to an instance's additive array methods. Processing begins when you call q.start().

npm install queue

npm test npm run test-browser

npm run example

var queue = require('queue');
var q = queue();
var results = [];
// add jobs using the Array API 
q.push(function(cb) {
  function(cb) {
  function(cb) {
q.unshift(function(cb) {
q.splice(2, 0, function(cb) {
// use the timeout feature to deal with jobs that 
// take too long or forget to execute a callback 
q.timeout = 100;
q.on('timeout', function(next, job) {
  console.log('job timed out:', job.toString().replace(/\n/g, ''));
q.push(function(cb) {
  setTimeout(function() {
    console.log('slow job finished');
  }, 200);
q.push(function(cb) {
  console.log('forgot to execute callback');
// get notified when jobs complete 
q.on('success', function(result, job) {
  console.log('job finished processing:', job.toString().replace(/\n/g, ''));
// begin processing, get notified on end / failure 
q.start(function(err) {
  console.log('all done:', results);

Where opts may contain inital values for:

  • q.concurrency
  • q.timeout

cb, if passed, will be called when the queue empties or when an error occurs.

Stops the queue. can be resumed with q.start().

Stop and empty the queue immediately.

Mozilla has docs on how these methods work here.

Max number of jobs the queue should process concurrently, defaults to Infinity.

Milliseconds to wait for a job to execute its callback.

Jobs pending + jobs to process (readonly).

After a job executes its callback.

After a job passes an error to its callback.

After q.timeout milliseconds have elapsed and a job has not executed its callback.

After all jobs have been processed

The latest stable release is published to npm. Abbreviated changelog below:

  • 4.0
  • Change license to MIT
  • 3.1.x
  • Add .npmignore
  • 3.0.x
  • Change the default concurrency to Infinity
  • Allow q.start() to accept an optional callback executed on q.emit('end')
  • 2.x
  • Major api changes / not backwards compatible with 1.x
  • 1.x
  • Early prototype

Copyright © 2014 Jesse Tane

This work is free. You can redistribute it and/or modify it under the terms of the MIT License. See LICENSE for full details.