Test if a value is undefined.
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> Test if a value is undefined.
``bash`
npm install @stdlib/assert-is-undefined
`javascript`
var isUndefined = require( '@stdlib/assert-is-undefined' );
#### isUndefined( value )
Tests if a value is undefined.
`javascript`
var bool = isUndefined( undefined );
// returns true
`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
`
*
- [@stdlib/assert-is-null][@stdlib/assert/is-null]: test if a value is null.
- [@stdlib/assert-is-undefined-or-null][@stdlib/assert/is-undefined-or-null]: test if a value is undefined or null.
*
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].
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---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
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