npm package: @stdlib/iter-unshift
Description: Create an iterator which prepends values to the beginning of a provided iterator.
Author: The Stdlib Authors
Latest version: 0.2.3

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<details>
  <summary>
    About stdlib...
  </summary>
  <p>We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.</p>
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# iterUnshift

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Create an [iterator][mdn-iterator-protocol] which prepends values to the beginning of a provided [iterator][mdn-iterator-protocol].

<!-- 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/iter-unshift
```

</section>

<section class="usage">

## Usage

```javascript
var iterUnshift = require( '@stdlib/iter-unshift' );
```

#### iterUnshift( iterator, ...items )

Returns an [iterator][mdn-iterator-protocol] which prepends values to the **beginning** of a provided [`iterator`][mdn-iterator-protocol].

```javascript
var array2iterator = require( '@stdlib/array-to-iterator' );

var it = iterUnshift( array2iterator( [ 1, 2 ] ), 3, 4 );
// returns <Object>

var v = it.next().value;
// returns 3

v = it.next().value;
// returns 4

v = it.next().value;
// returns 1

v = it.next().value;
// returns 2

var bool = it.next().done;
// returns true
```

The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:

-   **next**: function which returns an [iterator][mdn-iterator-protocol] protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the [iterator][mdn-iterator-protocol] is finished.
-   **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.

</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">

## Notes

-   If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-iter-randu' );
var iterUnshift = require( '@stdlib/iter-unshift' );

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 10
});

// Create an iterator with prepended values:
var it = iterUnshift( rand, 'beep', 'boop' );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
        break;
    }
    console.log( v.value );
}
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/iter-concat`][@stdlib/iter/concat]</span><span class="delimiter">: </span><span class="description">create an iterator which iterates over the values of two or more iterators.</span>
-   <span class="package-name">[`@stdlib/iter-push`][@stdlib/iter/push]</span><span class="delimiter">: </span><span class="description">create an iterator which appends additional values to the end of a provided iterator.</span>
-   <span class="package-name">[`@stdlib/iter-shift`][@stdlib/iter/shift]</span><span class="delimiter">: </span><span class="description">create an iterator which skips the first value of a provided iterator.</span>

</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

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

</section>

<!-- /.stdlib -->

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<section class="links">

[npm-image]: http://img.shields.io/npm/v/@stdlib/iter-unshift.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter-unshift

[test-image]: https://github.com/stdlib-js/iter-unshift/actions/workflows/test.yml/badge.svg?branch=v0.2.3
[test-url]: https://github.com/stdlib-js/iter-unshift/actions/workflows/test.yml?query=branch:v0.2.3

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/iter-unshift/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/iter-unshift?branch=main

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[stdlib]: https://github.com/stdlib-js/stdlib

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[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/iter-unshift/tree/deno
[deno-readme]: https://github.com/stdlib-js/iter-unshift/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/iter-unshift/tree/umd
[umd-readme]: https://github.com/stdlib-js/iter-unshift/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/iter-unshift/tree/esm
[esm-readme]: https://github.com/stdlib-js/iter-unshift/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/iter-unshift/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter-unshift/main/LICENSE

[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

<!-- <related-links> -->

[@stdlib/iter/concat]: https://www.npmjs.com/package/@stdlib/iter-concat

[@stdlib/iter/push]: https://www.npmjs.com/package/@stdlib/iter-push

[@stdlib/iter/shift]: https://www.npmjs.com/package/@stdlib/iter-shift

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</section>

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