https://github.com/stdlib-js/utils-fifo
First-in-first-out (FIFO) queue.
https://github.com/stdlib-js/utils-fifo
collection data data-structure data-structures fifo first-in first-out javascript node node-js nodejs queue stdlib structure util utilities utility utils
Last synced: 2 months ago
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First-in-first-out (FIFO) queue.
- Host: GitHub
- URL: https://github.com/stdlib-js/utils-fifo
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-14T16:57:11.000Z (over 4 years ago)
- Default Branch: main
- Last Pushed: 2025-01-20T01:30:29.000Z (9 months ago)
- Last Synced: 2025-07-12T22:36:28.290Z (3 months ago)
- Topics: collection, data, data-structure, data-structures, fifo, first-in, first-out, javascript, node, node-js, nodejs, queue, stdlib, structure, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 498 KB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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# FIFO
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> First-in-first-out (FIFO) queue.
## Installation
```bash
npm install @stdlib/utils-fifo
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage
```javascript
var fifo = require( '@stdlib/utils-fifo' );
```
#### fifo()
Returns a new first-in-first-out (FIFO) queue instance.
```javascript
var queue = fifo();
// returns
```
##### queue.clear()
Clears a queue.
```javascript
var queue = fifo();
// returns
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Peek at the first value:
var v = queue.first();
// returns 'foo'
// Examine the queue length:
var len = queue.length;
// returns 2
// Clear all queue items:
queue.clear();
// Peek at the first value:
v = queue.first();
// returns undefined
// Examine the queue length:
len = queue.length;
// returns 0
```
##### queue.first()
Returns the "oldest" queue value (i.e., the value which is "first-out"). If the queue is currently empty, the returned value is `undefined`.
```javascript
var queue = fifo();
// returns
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Peek at the first value:
var v = queue.first();
// returns 'foo'
```
##### queue.iterator()
Returns an iterator for iterating over a queue. If an environment supports `Symbol.iterator`, the returned iterator is iterable.
```javascript
var queue = fifo();
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Create an iterator:
var it = queue.iterator();
// Iterate over the queue...
var v = it.next().value;
// returns 'foo'
v = it.next().value;
// returns 'bar'
var bool = it.next().done;
// returns true
```
**Note**: in order to prevent confusion arising from queue mutation during iteration, a returned iterator **always** iterates over a queue "snapshot", which is defined as the list of queue elements at the time of `queue.iterator()` invocation.
##### queue.last()
Returns the "newest" queue value (i.e., the value which is "last-out"). If the queue is currently empty, the returned value is `undefined`.
```javascript
var queue = fifo();
// returns
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Peek at the last value:
var v = queue.last();
// returns 'bar'
```
##### queue.length
Queue length.
```javascript
var queue = fifo();
// Examine the initial queue length:
var len = queue.length;
// returns 0
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Retrieve the current queue length:
len = queue.length;
// returns 2
```
##### queue.pop()
Removes a value from the queue. If the queue is currently empty, the returned value is `undefined`.
```javascript
var queue = fifo();
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Remove the first value:
var v = queue.pop();
// returns 'foo'
// Add a new value to the queue:
queue.push( 'beep' );
// Remove the "oldest" queue value:
v = queue.pop();
// returns 'bar'
```
##### queue.push( value )
Adds a value to the queue.
```javascript
var queue = fifo();
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Remove the first value:
var v = queue.pop();
// returns 'foo'
// Add a new value to the queue:
queue.push( 'beep' );
// Remove the "oldest" queue value:
v = queue.pop();
// returns 'bar'
```
##### queue.toArray()
Returns an array of queue values.
```javascript
var queue = fifo();
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Get an array of queue values:
var vals = queue.toArray();
// returns [ 'foo', 'bar' ]
```
##### queue.toJSON()
Serializes a queue as JSON.
```javascript
var queue = fifo();
// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );
// Serialize to JSON:
var o = queue.toJSON();
// returns { 'type': 'fifo', 'data': [ 'foo', 'bar' ] }
```
**Note**: `JSON.stringify()` implicitly calls this method when stringifying a queue instance.
## Examples
```javascript
var fifo = require( '@stdlib/utils-fifo' );
var queue;
var iter;
var len;
var v;
var i;
// Create a new FIFO queue:
queue = fifo();
// Add some values to the queue:
queue.push( 'foo' );
queue.push( 'bar' );
queue.push( 'beep' );
queue.push( 'boop' );
// Peek at the first and last queue values:
v = queue.first();
// returns 'foo'
v = queue.last();
// returns 'boop'
// Inspect the queue length:
len = queue.length;
// returns 4
// Remove the "oldest" queue value:
v = queue.pop();
// returns 'foo'
// Inspect the queue length:
len = queue.length;
// returns 3
// Iterate over the queue:
iter = queue.iterator();
for ( i = 0; i < len; i++ ) {
console.log( 'Queue value #%d: %s', i+1, iter.next().value );
}
// Clear the queue:
queue.clear();
// Inspect the queue length:
len = queue.length;
// returns 0
```
* * *
## See Also
- [`@stdlib/utils-stack`][@stdlib/utils/stack]: stack.
* * *
## Notice
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-fifo.svg
[npm-url]: https://npmjs.org/package/@stdlib/utils-fifo
[test-image]: https://github.com/stdlib-js/utils-fifo/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/utils-fifo/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-fifo/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/utils-fifo?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/utils-fifo/tree/deno
[deno-readme]: https://github.com/stdlib-js/utils-fifo/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/utils-fifo/tree/umd
[umd-readme]: https://github.com/stdlib-js/utils-fifo/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/utils-fifo/tree/esm
[esm-readme]: https://github.com/stdlib-js/utils-fifo/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/utils-fifo/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-fifo/main/LICENSE
[@stdlib/utils/stack]: https://github.com/stdlib-js/utils-stack