npm package: @stdlib/iter-first
Description: Return the first iterated value.
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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</details>

# iterFirst

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

> Return the first [iterated][mdn-iterator-protocol] value.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/iter-first
```

</section>

<section class="usage">

## Usage

```javascript
var iterFirst = require( '@stdlib/iter-first' );
```

#### iterFirst( iterator )

Returns the first [iterated][mdn-iterator-protocol] value.

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

var arr = array2iterator( [ 1, 0, 0, 0, 0 ] );

var v = iterFirst( arr );
// returns 1
```

If a provided [`iterator`][mdn-iterator-protocol] does not return any [iterated][mdn-iterator-protocol] values, the function returns `undefined`.

```javascript
var iterEmpty = require( '@stdlib/iter-empty' );

var v = iterFirst( iterEmpty() );
// returns undefined
```

</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

-   The function does **not** consume an entire [iterator][mdn-iterator-protocol] before returning.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random-iter-randu' );
var iterMap = require( '@stdlib/iter-map' );
var iterFirst = require( '@stdlib/iter-first' );

function threshold( r ) {
    return ( r > 0.95 );
}

// Create an iterator which generates uniformly distributed pseudorandom numbers:
var opts = {
    'iter': 100
};
var riter = randu( opts );

// Create an iterator which applies a threshold to generated numbers:
var miter = iterMap( riter, threshold );

// Return the first threshold result:
var bool = iterFirst( miter );
// returns <boolean>

console.log( bool );
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/iter-head`][@stdlib/iter/head]</span><span class="delimiter">: </span><span class="description">create an iterator which returns the first `n` values of a provided iterator.</span>
-   <span class="package-name">[`@stdlib/iter-last`][@stdlib/iter/last]</span><span class="delimiter">: </span><span class="description">consume an entire iterator and return the last iterated value.</span>
-   <span class="package-name">[`@stdlib/iter-nth`][@stdlib/iter/nth]</span><span class="delimiter">: </span><span class="description">return the nth iterated value.</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-first.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter-first

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

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

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

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

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

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

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

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

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

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

</section>

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