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Asynchronous function queue with adjustable concurrency.
This module exports a class Queue that implements most of the Array API. Pass async functions (ones that accept a callback or return a promise) to an instance's additive array methods. Processing begins when you call q.start().
Example
npm run example
var queue = require('../')
var q = queue({ results: [] })
// add jobs using the familiar Array API
q.push(function (cb) {
const result = 'two'
cb(null, result)
})
q.push(
function (cb) {
const result = 'four'
cb(null, result)
},
function (cb) {
const result = 'five'
cb(null, result)
}
)
// jobs can accept a callback or return a promise
q.push(function () {
return new Promise(function (resolve, reject) {
const result = 'one'
resolve(result)
})
})
q.unshift(function (cb) {
const result = 'one'
cb(null, result)
})
q.splice(2, 0, function (cb) {
const result = 'three'
cb(null, result)
})
// 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, ''))
next()
})
q.push(function (cb) {
setTimeout(function () {
console.log('slow job finished')
cb()
}, 200)
})
q.push(function (cb) {
console.log('forgot to execute callback')
})
// jobs can also override the queue's timeout
// on a per-job basis
function extraSlowJob (cb) {
setTimeout(function () {
console.log('extra slow job finished')
cb()
}, 400)
}
extraSlowJob.timeout = 500
q.push(extraSlowJob)
// jobs can also opt-out of the timeout altogether
function superSlowJob (cb) {
setTimeout(function () {
console.log('super slow job finished')
cb()
}, 1000)
}
superSlowJob.timeout = null
q.push(superSlowJob)
// get notified when jobs complete
q.on('success', function (result, job) {
console.log('job finished processing:', job.toString().replace(/\n/g, ''))
console.log('The result is:', result)
})
// begin processing, get notified on end / failure
q.start(function (err) {
if (err) throw err
console.log('all done:', q.results)
})
Install
npm install queue
Note: You may need to install the events dependency if your environment does not have it by default (eg. browser, react-native).
Test
npm test npm run test-browser
API
var q = queue([opts])
Constructor. opts may contain inital values for:
q.concurrencyq.timeoutq.autostartq.results
Instance methods
q.start([cb])
cb, if passed, will be called when the queue empties or when an error occurs.
q.stop()
Stops the queue. can be resumed with q.start().
q.end([err])
Stop and empty the queue immediately.
Instance methods mixed in from Array
Mozilla has docs on how these methods work here. Note that slice does not copy the queue.
q.push(element1, ..., elementN)
q.unshift(element1, ..., elementN)
q.splice(index , howMany[, element1[, ...[, elementN]]])
q.pop()
q.shift()
q.slice(begin[, end])
q.reverse()
q.indexOf(searchElement[, fromIndex])
q.lastIndexOf(searchElement[, fromIndex])
Properties
q.concurrency
Max number of jobs the queue should process concurrently, defaults to Infinity.
q.timeout
Milliseconds to wait for a job to execute its callback. This can be overridden by specifying a timeout property on a per-job basis.
q.autostart
Ensures the queue is always running if jobs are available. Useful in situations where you are using a queue only for concurrency control.
q.results
An array to set job callback arguments on.
q.length
Jobs pending + jobs to process (readonly).
Events
q.emit('start', job)
Immediately before a job begins to execute.
q.emit('success', result, job)
After a job executes its callback.
q.emit('error', err, job)
After a job passes an error to its callback.
q.emit('timeout', continue, job)
After q.timeout milliseconds have elapsed and a job has not executed its callback.
q.emit('end'[, err])
After all jobs have been processed
Releases
The latest stable release is published to npm. Abbreviated changelog below:
- 6.0
- Add
startevent before job begins (@joelgriffith) - Add
timeoutproperty on a job to override the queue's timeout (@joelgriffith)
- Add
- 5.0
- Updated TypeScript bindings (@Codex-)
- 4.4
- Add results feature
- 4.3
- Add promise support (@kwolfy)
- 4.2
- Unref timers on end
- 4.1
- Add autostart feature
- 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 onq.emit('end')
- Change the default concurrency to
- 2.x
- Major api changes / not backwards compatible with 1.x
- 1.x
- Early prototype
License
Copyright © 2014 Jesse Tane [email protected]
This work is free. You can redistribute it and/or modify it under the terms of the MIT License. See LICENSE for full details.