The isPrototypeOf()
method checks if an object exists in another object's prototype chain.
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isPrototypeOf()
differs from the instanceof
operator. In the expression "object instanceof AFunction
", the object
prototype chain is checked against AFunction.prototype
, not against AFunction
itself.
Syntax
prototypeObj.isPrototypeOf(object)
Parameters
object
- The object whose prototype chain will be searched.
Return value
A Boolean
indicating whether the calling object lies in the prototype chain of the specified object.
Errors thrown
Description
The isPrototypeOf()
method allows you to check whether or not an object exists within another object's prototype chain.
Examples
Using isPrototypeOf
This example demonstrates that Baz.prototype
, Bar.prototype
, Foo.prototype
and Object.prototype
exist in the prototype chain for object baz
:
function Foo() {} function Bar() {} function Baz() {} Bar.prototype = Object.create(Foo.prototype); Baz.prototype = Object.create(Bar.prototype); var baz = new Baz(); console.log(Baz.prototype.isPrototypeOf(baz)); // true console.log(Bar.prototype.isPrototypeOf(baz)); // true console.log(Foo.prototype.isPrototypeOf(baz)); // true console.log(Object.prototype.isPrototypeOf(baz)); // true
isPrototypeOf()
method, along with the instanceof
operator particularly comes in handy if you have code that can only function when dealing with objects descended from a specific prototype chain, e.g., to guarantee that certain methods or properties will be present on that object.
For example, check if baz
object descends from Foo.prototype
:
if (Foo.prototype.isPrototypeOf(baz)) { // do something safe }
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'Object.prototype.isPrototypeOf' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
isPrototypeOf | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 9 | Opera Full support 4 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support