@stdlib/assert-is-prototype-of
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0.2.1 • Public • Published
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isPrototypeOf

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

Installation

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

Usage

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

isPrototypeOf( obj, prototype )

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

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.

    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.

    var bool = isPrototypeOf( Object.create( null ), null );
    // throws <TypeError>
  • isPrototypeOf() is generally more robust than the instanceof operator. Consider the following example which does not use constructors:

    // 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

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


Notice

This package is part of 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, see the main project repository.

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.

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