npm package: @stdlib/assert-is-undefined
Description: Test if a value is undefined.
Author: The Stdlib Authors
Latest version: 0.2.3

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<details>
  <summary>
    About stdlib...
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# isUndefined

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

> Test if a value is undefined.

<section class="installation">

## Installation

```bash
npm install @stdlib/assert-is-undefined
```

</section>

<section class="usage">

## Usage

```javascript
var isUndefined = require( '@stdlib/assert-is-undefined' );
```

#### isUndefined( value )

Tests if a `value` is `undefined`.

<!-- eslint-disable no-undefined -->

```javascript
var bool = isUndefined( undefined );
// returns true
```

</section>

<!-- /.usage -->

<section class="examples">

## Examples

<!-- eslint-disable no-undefined, no-restricted-syntax, no-empty-function -->

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

```javascript
var isUndefined = require( '@stdlib/assert-is-undefined' );

var bool;
var x;

bool = isUndefined( x );
// returns true

bool = isUndefined( undefined );
// returns true

bool = isUndefined( void 0 );
// returns true

bool = isUndefined( 'beep' );
// returns false

bool = isUndefined( 5 );
// returns false

bool = isUndefined( null );
// returns false

bool = isUndefined( true );
// returns false

bool = isUndefined( {} );
// returns false

bool = isUndefined( [] );
// returns false

bool = isUndefined( function foo() {} );
// returns false
```

</section>

<!-- /.examples -->

<!-- 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/assert-is-null`][@stdlib/assert/is-null]</span><span class="delimiter">: </span><span class="description">test if a value is null.</span>
-   <span class="package-name">[`@stdlib/assert-is-undefined-or-null`][@stdlib/assert/is-undefined-or-null]</span><span class="delimiter">: </span><span class="description">test if a value is undefined or null.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<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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[npm-image]: http://img.shields.io/npm/v/@stdlib/assert-is-undefined.svg
[npm-url]: https://npmjs.org/package/@stdlib/assert-is-undefined

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

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/assert-is-undefined/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/assert-is-undefined?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/assert-is-undefined/tree/deno
[deno-readme]: https://github.com/stdlib-js/assert-is-undefined/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/assert-is-undefined/tree/umd
[umd-readme]: https://github.com/stdlib-js/assert-is-undefined/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/assert-is-undefined/tree/esm
[esm-readme]: https://github.com/stdlib-js/assert-is-undefined/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/assert-is-undefined/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/assert-is-undefined/main/LICENSE

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

[@stdlib/assert/is-null]: https://www.npmjs.com/package/@stdlib/assert-is-null

[@stdlib/assert/is-undefined-or-null]: https://www.npmjs.com/package/@stdlib/assert-is-undefined-or-null

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

</section>

<!-- /.links -->