@stdlib/assert/instance-of/README.md

Standard assertion utilities.

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# instanceOf

> Test whether a value has in its prototype chain a specified constructor as a prototype property.

<section class="intro">

</section>

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<section class="usage">

## Usage

```javascript
var instanceOf = require( '@stdlib/assert/instance-of' );
```

#### instanceOf( value, constructor )

Tests whether a `value` has in its prototype chain a specified `constructor` as a `prototype` property.

```javascript
var inherit = require( '@stdlib/utils/inherit' );

function Foo() {
    return this;
}

function Bar() {
    return this;
}
inherit( Bar, Foo );

var bar = new Bar();

var bool = instanceOf( bar, Foo );
// returns true
```

</section>

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<section class="notes">

## Notes

-   The function throws a `TypeError` if provided a `constructor` argument which is not callable.

    ```javascript
    var bool = instanceOf( {}, null );
    // throws <TypeError>
    ```

-   While the prototype of an `object` created using object literal notion is `undefined`, the function returns `true` when provided an `object` literal and the `Object` constructor. This maintains consistent behavior with the `instanceof` operator.

    <!-- FIXME: apparent issue with realms when linting doctest values -->

    <!-- eslint-disable stdlib/doctest -->

    ```javascript
    var Object = require( '@stdlib/object/ctor' );

    var bool = ( {} instanceof Object );
    // returns true

    bool = instanceOf( {}, Object );
    // returns true
    ```

</section>

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<section class="examples">

## Examples

<!-- FIXME: apparent issue with realms when linting doctest values -->

<!-- eslint-disable stdlib/doctest -->

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

```javascript
var Number = require( '@stdlib/number/ctor' );
var Object = require( '@stdlib/object/ctor' );
var Function = require( '@stdlib/function/ctor' );
var instanceOf = require( '@stdlib/assert/instance-of' );

var bool = instanceOf( [], Array );
// returns true

bool = instanceOf( [], Object );
// returns true

bool = instanceOf( {}, Object );
// returns true

bool = instanceOf( new Date(), Date );
// returns true

bool = instanceOf( /.*/, RegExp );
// returns true

bool = instanceOf( instanceOf, Function );
// returns true

bool = instanceOf( null, Object );
// returns false

bool = instanceOf( 5, Number );
// returns false

bool = instanceOf( '5', String );
// returns false

bool = instanceOf( void 0, Object );
// returns false

bool = instanceOf( {}, Array );
// returns false

bool = instanceOf( {}, Function );
// returns false
```

</section>

<!-- /.examples -->

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/assert/is-prototype-of`][@stdlib/assert/is-prototype-of]</span><span class="delimiter">: </span><span class="description">test if an object's prototype chain contains a provided prototype.</span>
-   <span class="package-name">[`@stdlib/utils/constructor-name`][@stdlib/utils/constructor-name]</span><span class="delimiter">: </span><span class="description">determine the name of a value's constructor.</span>
-   <span class="package-name">[`@stdlib/utils/inherit`][@stdlib/utils/inherit]</span><span class="delimiter">: </span><span class="description">implement prototypical inheritance by replacing the prototype of one constructor with the prototype of another constructor.</span>
-   <span class="package-name">[`@stdlib/utils/type-of`][@stdlib/utils/type-of]</span><span class="delimiter">: </span><span class="description">determine a value's type.</span>

</section>

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

[@stdlib/assert/is-prototype-of]: https://github.com/stdlib-js/assert/tree/main/is-prototype-of

[@stdlib/utils/constructor-name]: https://www.npmjs.com/package/@stdlib/utils-constructor-name

[@stdlib/utils/inherit]: https://www.npmjs.com/package/@stdlib/utils-inherit

[@stdlib/utils/type-of]: https://www.npmjs.com/package/@stdlib/utils-type-of

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