asynchronous function queue with adjustable concurrency
npm install queue``
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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().
or npm run dev and open the example directory (and your console) to run the following program:
` javascript
import Queue from 'queue'const q = new Queue({ results: [] })
// add jobs using the familiar Array API
q.push(cb => {
const result = 'two'
cb(null, result)
})
q.push(
cb => {
const result = 'four'
cb(null, result)
},
cb => {
const result = 'five'
cb(null, result)
}
)
// jobs can accept a callback or return a promise
q.push(() => {
return new Promise((resolve, reject) => {
const result = 'one'
resolve(result)
})
})
q.unshift(cb => {
const result = 'one'
cb(null, result)
})
q.splice(2, 0, 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.addEventListener('timeout', e => {
console.log('job timed out:', e.detail.job.toString().replace(/\n/g, ''))
e.detail.next()
})
q.push(cb => {
setTimeout(() => {
console.log('slow job finished')
cb()
}, 200)
})
q.push(cb => {
console.log('forgot to execute callback')
})
// jobs can also override the queue's timeout
// on a per-job basis
function extraSlowJob (cb) {
setTimeout(() => {
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(() => {
console.log('super slow job finished')
cb()
}, 1000)
}
superSlowJob.timeout = null
q.push(superSlowJob)
// get notified when jobs complete
q.addEventListener('success', e => {
console.log('job finished processing:', e.detail.toString().replace(/\n/g, ''))
console.log('The result is:', e.detail.result)
})
// begin processing, get notified on end / failure
q.start(err => {
if (err) throw err
console.log('all done:', q.results)
})
`Install
npm install queueyarn add queue
Test
npm testnpm run dev // for testing in a browser, open test directory (and your console)
API
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Constructor. may contain initial values for:
* q.concurrency
*
*
* Instance methods
$3
Explicitly starts processing jobs and provides feedback to the caller when the queue empties or an error occurs. If cb is not passed a promise will be returned.$3
Stops the queue. can be resumed with .$3
Stop and empty the queue immediately.Instance methods mixed in from
Array
Mozilla has docs on how these methods work here. Note that does not copy the queue.
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Properties
$3
Max number of jobs the queue should process concurrently, defaults to Infinity.$3
Milliseconds to wait for a job to execute its callback. This can be overridden by specifying a timeout property on a per-job basis.$3
Ensures the queue is always running if jobs are available. Useful in situations where you are using a queue only for concurrency control.$3
An array to set job callback arguments on.$3
Jobs pending + jobs to process (readonly).Events
$3
Immediately before a job begins to execute.$3
After a job executes its callback.$3
After a job passes an error to its callback.$3
After q.timeout milliseconds have elapsed and a job has not executed its callback.$3
After all jobs have been processedReleases
The latest stable release is published to npm. Abbreviated changelog below:
* 7.0
* Modernized codebase, added new maintainer (@MaksimLavrenyuk)
* 6.0
* Add start event before job begins (@joelgriffith)
* Add timeout property on a job to override the queue's timeout (@joelgriffith)
* 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 to accept an optional callback executed on q.emit('end')`