Reflect.setPrototypeOf()

The Reflect.setPrototypeOf() static method is like Object.setPrototypeOf() but returns a Boolean. It sets the prototype (i.e., the internal [[Prototype]] property) of a specified object.

Try it

const object1 = {};

console.log(Reflect.setPrototypeOf(object1, Object.prototype));
// Expected output: true

console.log(Reflect.setPrototypeOf(object1, null));
// Expected output: true

const object2 = {};

console.log(Reflect.setPrototypeOf(Object.freeze(object2), null));
// Expected output: false

Syntax

js
Reflect.setPrototypeOf(target, prototype)

Parameters

target

The target object of which to set the prototype.

prototype

The object's new prototype (an object or null).

Return value

A Boolean indicating whether or not the prototype was successfully set.

Exceptions

TypeError

Thrown if target is not an object or if prototype is neither an object nor null.

Description

Reflect.setPrototypeOf() provides the reflective semantic of setting the prototype of an object. At the very low level, setting the prototype returns a boolean (as is the case with the proxy handler). Object.setPrototypeOf() provides nearly the same semantic, but it throws a TypeError if the status is false (the operation was unsuccessful), while Reflect.setPrototypeOf() directly returns the status.

Reflect.setPrototypeOf() invokes the [[SetPrototypeOf]] object internal method of target.

Examples

undefined

Using Reflect.setPrototypeOf()

js
Reflect.setPrototypeOf({}, Object.prototype); // true

// It can change an object's [[Prototype]] to null.
Reflect.setPrototypeOf({}, null); // true

// Returns false if target is not extensible.
Reflect.setPrototypeOf(Object.freeze({}), null); // false

// Returns false if it cause a prototype chain cycle.
const target = {};
const proto = Object.create(target);
Reflect.setPrototypeOf(target, proto); // false

Specifications

See also