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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()
.
Do npm run example
or npm run dev
and open the example directory (and your console) to run the following program:
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)
})
npm install queue
yarn add queue
npm test
npm run dev // for testing in a browser, open test directory (and your console)
const q = new Queue([opts])
Constructor. opts
may contain initial values for:
q.concurrency
q.timeout
q.autostart
q.results
q.start([cb])
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.
q.stop()
Stops the queue. can be resumed with q.start()
.
q.end([err])
Stop and empty the queue immediately.
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])
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).
q.dispatchEvent(new QueueEvent('start', { job }))
Immediately before a job begins to execute.
q.dispatchEvent(new QueueEvent('success', { result: [...result], job }))
After a job executes its callback.
q.dispatchEvent(new QueueEvent('error', { err, job }))
After a job passes an error to its callback.
q.dispatchEvent(new QueueEvent('timeout', { next, job }))
After q.timeout
milliseconds have elapsed and a job has not executed its callback.
q.dispatchEvent(new QueueEvent('end', { err }))
After all jobs have been processed
The latest stable release is published to npm. Abbreviated changelog below:
start
event before job begins (@joelgriffith)timeout
property on a job to override the queue's timeout (@joelgriffith)Infinity
q.start()
to accept an optional callback executed on q.emit('end')