Reflect.setPrototypeOf()

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.

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

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.

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

Using Reflect.setPrototypeOf()

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

Specification
ECMAScript® 2026 Language Specification # sec-reflect.setprototypeof