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# fastq
![ci][ci-url]
[![npm version][npm-badge]][npm-url]
[![Dependency Status][david-badge]][david-url]
Fast, in memory work queue.
Benchmarks (1 million tasks):
* setImmediate: 812ms
* fastq: 854ms
* async.queue: 1298ms
* neoAsync.queue: 1249ms
Obtained on node 12.16.1, on a dedicated server.
If you need zero-overhead series function call, check out
[fastseries](http://npm.im/fastseries). For zero-overhead parallel
function call, check out [fastparallel](http://npm.im/fastparallel).
[![js-standard-style](https://raw.githubusercontent.com/feross/standard/master/badge.png)](https://github.com/feross/standard)
* <a href="#install">Installation</a>
* <a href="#usage">Usage</a>
* <a href="#api">API</a>
* <a href="#license">Licence &amp; copyright</a>
## Install
`npm i fastq --save`
## Usage (callback API)
```js
'use strict'
const queue = require('fastq')(worker, 1)
queue.push(42, function (err, result) {
if (err) { throw err }
console.log('the result is', result)
})
function worker (arg, cb) {
cb(null, arg * 2)
}
```
## Usage (promise API)
```js
const queue = require('fastq').promise(worker, 1)
async function worker (arg) {
return arg * 2
}
async function run () {
const result = await queue.push(42)
console.log('the result is', result)
}
run()
```
### Setting "this"
```js
'use strict'
const that = { hello: 'world' }
const queue = require('fastq')(that, worker, 1)
queue.push(42, function (err, result) {
if (err) { throw err }
console.log(this)
console.log('the result is', result)
})
function worker (arg, cb) {
console.log(this)
cb(null, arg * 2)
}
```
### Using with TypeScript (callback API)
```ts
'use strict'
import * as fastq from "fastq";
import type { queue, done } from "fastq";
type Task = {
id: number
}
const q: queue<Task> = fastq(worker, 1)
q.push({ id: 42})
function worker (arg: Task, cb: done) {
console.log(arg.id)
cb(null)
}
```
### Using with TypeScript (promise API)
```ts
'use strict'
import * as fastq from "fastq";
import type { queueAsPromised } from "fastq";
type Task = {
id: number
}
const q: queueAsPromised<Task> = fastq.promise(asyncWorker, 1)
q.push({ id: 42}).catch((err) => console.error(err))
async function asyncWorker (arg: Task): Promise<void> {
// No need for a try-catch block, fastq handles errors automatically
console.log(arg.id)
}
```
## API
* <a href="#fastqueue"><code>fastqueue()</code></a>
* <a href="#push"><code>queue#<b>push()</b></code></a>
* <a href="#unshift"><code>queue#<b>unshift()</b></code></a>
* <a href="#pause"><code>queue#<b>pause()</b></code></a>
* <a href="#resume"><code>queue#<b>resume()</b></code></a>
* <a href="#idle"><code>queue#<b>idle()</b></code></a>
* <a href="#length"><code>queue#<b>length()</b></code></a>
* <a href="#getQueue"><code>queue#<b>getQueue()</b></code></a>
* <a href="#kill"><code>queue#<b>kill()</b></code></a>
* <a href="#killAndDrain"><code>queue#<b>killAndDrain()</b></code></a>
* <a href="#error"><code>queue#<b>error()</b></code></a>
* <a href="#concurrency"><code>queue#<b>concurrency</b></code></a>
* <a href="#drain"><code>queue#<b>drain</b></code></a>
* <a href="#empty"><code>queue#<b>empty</b></code></a>
* <a href="#saturated"><code>queue#<b>saturated</b></code></a>
* <a href="#promise"><code>fastqueue.promise()</code></a>
-------------------------------------------------------
<a name="fastqueue"></a>
### fastqueue([that], worker, concurrency)
Creates a new queue.
Arguments:
* `that`, optional context of the `worker` function.
* `worker`, worker function, it would be called with `that` as `this`,
if that is specified.
* `concurrency`, number of concurrent tasks that could be executed in
parallel.
-------------------------------------------------------
<a name="push"></a>
### queue.push(task, done)
Add a task at the end of the queue. `done(err, result)` will be called
when the task was processed.
-------------------------------------------------------
<a name="unshift"></a>
### queue.unshift(task, done)
Add a task at the beginning of the queue. `done(err, result)` will be called
when the task was processed.
-------------------------------------------------------
<a name="pause"></a>
### queue.pause()
Pause the processing of tasks. Currently worked tasks are not
stopped.
-------------------------------------------------------
<a name="resume"></a>
### queue.resume()
Resume the processing of tasks.
-------------------------------------------------------
<a name="idle"></a>
### queue.idle()
Returns `false` if there are tasks being processed or waiting to be processed.
`true` otherwise.
-------------------------------------------------------
<a name="length"></a>
### queue.length()
Returns the number of tasks waiting to be processed (in the queue).
-------------------------------------------------------
<a name="getQueue"></a>
### queue.getQueue()
Returns all the tasks be processed (in the queue). Returns empty array when there are no tasks
-------------------------------------------------------
<a name="kill"></a>
### queue.kill()
Removes all tasks waiting to be processed, and reset `drain` to an empty
function.
-------------------------------------------------------
<a name="killAndDrain"></a>
### queue.killAndDrain()
Same than `kill` but the `drain` function will be called before reset to empty.
-------------------------------------------------------
<a name="error"></a>
### queue.error(handler)
Set a global error handler. `handler(err, task)` will be called
each time a task is completed, `err` will be not null if the task has thrown an error.
-------------------------------------------------------
<a name="concurrency"></a>
### queue.concurrency
Property that returns the number of concurrent tasks that could be executed in
parallel. It can be altered at runtime.
-------------------------------------------------------
<a name="drain"></a>
### queue.drain
Function that will be called when the last
item from the queue has been processed by a worker.
It can be altered at runtime.
-------------------------------------------------------
<a name="empty"></a>
### queue.empty
Function that will be called when the last
item from the queue has been assigned to a worker.
It can be altered at runtime.
-------------------------------------------------------
<a name="saturated"></a>
### queue.saturated
Function that will be called when the queue hits the concurrency
limit.
It can be altered at runtime.
-------------------------------------------------------
<a name="promise"></a>
### fastqueue.promise([that], worker(arg), concurrency)
Creates a new queue with `Promise` apis. It also offers all the methods
and properties of the object returned by [`fastqueue`](#fastqueue) with the modified
[`push`](#pushPromise) and [`unshift`](#unshiftPromise) methods.
Node v10+ is required to use the promisified version.
Arguments:
* `that`, optional context of the `worker` function.
* `worker`, worker function, it would be called with `that` as `this`,
if that is specified. It MUST return a `Promise`.
* `concurrency`, number of concurrent tasks that could be executed in
parallel.
<a name="pushPromise"></a>
#### queue.push(task) => Promise
Add a task at the end of the queue. The returned `Promise` will be fulfilled (rejected)
when the task is completed successfully (unsuccessfully).
This promise could be ignored as it will not lead to a `'unhandledRejection'`.
<a name="unshiftPromise"></a>
#### queue.unshift(task) => Promise
Add a task at the beginning of the queue. The returned `Promise` will be fulfilled (rejected)
when the task is completed successfully (unsuccessfully).
This promise could be ignored as it will not lead to a `'unhandledRejection'`.
<a name="drained"></a>
#### queue.drained() => Promise
Wait for the queue to be drained. The returned `Promise` will be resolved when all tasks in the queue have been processed by a worker.
This promise could be ignored as it will not lead to a `'unhandledRejection'`.
## License
ISC
[ci-url]: https://github.com/mcollina/fastq/workflows/ci/badge.svg
[npm-badge]: https://badge.fury.io/js/fastq.svg
[npm-url]: https://badge.fury.io/js/fastq
[david-badge]: https://david-dm.org/mcollina/fastq.svg
[david-url]: https://david-dm.org/mcollina/fastq
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