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https://github.com/stdlib-js/assert-is-prototype-of

Test if an object's prototype chain contains a provided prototype.
https://github.com/stdlib-js/assert-is-prototype-of

assert assertion class inherit inheritance inherits instanceof javascript node node-js nodejs object-oriented oop proto prototype stdlib util utilities utility utils

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Test if an object's prototype chain contains a provided prototype.

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README 

        



  

    About stdlib...

  

  
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When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.


  
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# isPrototypeOf



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



> Test if an object's prototype chain contains a provided prototype.



## Installation



```bash

npm install @stdlib/assert-is-prototype-of

```



Alternatively,



-   To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).

-   If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).

-   For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).



The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.



To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.



## Usage



```javascript

var isPrototypeOf = require( '@stdlib/assert-is-prototype-of' );

```



#### isPrototypeOf( obj, prototype )



Tests if an `object`'s prototype chain contains a provided `prototype`.



```javascript

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



function Foo() {

    return this;

}



function Bar() {

    return this;

}

inherit( Bar, Foo );



var bar = new Bar();



var bool = isPrototypeOf( bar, Foo.prototype );

// returns true

```



## Notes



-   The function returns `false` if provided a primitive value.



    



    ```javascript

    var Number = require( '@stdlib/number-ctor' );



    var bool = isPrototypeOf( 5, Number.prototype );

    // returns false



    bool = isPrototypeOf( 'beep', String.prototype );

    // returns false



    bool = isPrototypeOf( true, Boolean.prototype );

    // returns false

    ```



-   The function throws a `TypeError` if provided a `prototype` value which is neither an `object` (except `null`) or a `function`.



    



    ```javascript

    var bool = isPrototypeOf( Object.create( null ), null );

    // throws 

    ```



-   `isPrototypeOf()` is generally more robust than the `instanceof` operator. Consider the following example which does not use constructors:



    



    ```javascript

    // Functionally similar to `Object.create()`...

    function createObject( proto ) {

        function Ctor() {

            // Empty constructor...

        }

        Ctor.prototype = proto;

        return new Ctor();

    }

    var superProto = {

        'beep': 'beep'

    };



    var subProto = createObject( superProto );

    subProto.boop = 'boop';



    var v = createObject( subProto );



    var bool;

    try {

        bool = ( v instanceof superProto );

    } catch ( error ) {

        // Encountered a type error...

        console.error( error.message );

    }



    bool = isPrototypeOf( v, superProto );

    // returns true

    ```



## Examples



```javascript

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

var isPrototypeOf = require( '@stdlib/assert-is-prototype-of' );



function A() {

    return this;

}



function B() {

    return this;

}

inherit( B, A );



function C() {

    return this;

}

inherit( C, B );



function D() {

    return this;

}

inherit( D, C );



var a = new A();

var b = new B();

var c = new C();

var d = new D();



var bool = isPrototypeOf( d, C.prototype );

// returns true



bool = isPrototypeOf( d, B.prototype );

// returns true



bool = isPrototypeOf( d, A.prototype );

// returns true



bool = isPrototypeOf( c, B.prototype );

// returns true



bool = isPrototypeOf( c, A.prototype );

// returns true



bool = isPrototypeOf( c, D.prototype );

// returns false



bool = isPrototypeOf( b, A.prototype );

// returns true



bool = isPrototypeOf( b, C.prototype );

// returns false



bool = isPrototypeOf( b, D.prototype );

// returns false



bool = isPrototypeOf( a, B.prototype );

// returns false



bool = isPrototypeOf( a, C.prototype );

// returns false



bool = isPrototypeOf( a, D.prototype );

// returns false

```



* * *



## See Also



-   [`@stdlib/utils-get-prototype-of`][@stdlib/utils/get-prototype-of]: return the prototype of a provided object.



* * *



## 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 © 2016-2024. The Stdlib [Authors][stdlib-authors].



[npm-image]: http://img.shields.io/npm/v/@stdlib/assert-is-prototype-of.svg

[npm-url]: https://npmjs.org/package/@stdlib/assert-is-prototype-of



[test-image]: https://github.com/stdlib-js/assert-is-prototype-of/actions/workflows/test.yml/badge.svg?branch=main

[test-url]: https://github.com/stdlib-js/assert-is-prototype-of/actions/workflows/test.yml?query=branch:main



[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/assert-is-prototype-of/main.svg

[coverage-url]: https://codecov.io/github/stdlib-js/assert-is-prototype-of?branch=main



[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg

[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im



[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/assert-is-prototype-of/tree/deno

[deno-readme]: https://github.com/stdlib-js/assert-is-prototype-of/blob/deno/README.md

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

[umd-readme]: https://github.com/stdlib-js/assert-is-prototype-of/blob/umd/README.md

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

[esm-readme]: https://github.com/stdlib-js/assert-is-prototype-of/blob/esm/README.md

[branches-url]: https://github.com/stdlib-js/assert-is-prototype-of/blob/main/branches.md



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



[@stdlib/utils/get-prototype-of]: https://github.com/stdlib-js/utils-get-prototype-of