npm package: @stdlib/dstructs-fifo
Description: First-in-first-out (FIFO) queue.
Author: The Stdlib Authors
Latest version: 0.1.1

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<details>
  <summary>
    About stdlib...
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</details>

# FIFO

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> First-in-first-out (FIFO) queue.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/dstructs-fifo
```

</section>

<section class="usage">

## Usage

```javascript
var fifo = require( '@stdlib/dstructs-fifo' );
```

#### fifo()

Returns a new first-in-first-out (FIFO) queue instance.

```javascript
var queue = fifo();
// returns <FIFO>
```

##### queue.clear()

Clears a queue.

```javascript
var queue = fifo();
// returns <FIFO>

// 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 <FIFO>

// 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 <FIFO>

// 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.

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var fifo = require( '@stdlib/dstructs-fifo' );

// Create a new FIFO queue:
var 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:
var v = queue.first();
// returns 'foo'

v = queue.last();
// returns 'boop'

// Inspect the queue length:
var 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:
var iter = queue.iterator();
var i;
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
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/dstructs-stack`][@stdlib/dstructs/stack]</span><span class="delimiter">: </span><span class="description">stack.</span>

</section>

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* * *

## 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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[umd]: https://github.com/umdjs/umd
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/dstructs-fifo/main/LICENSE

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