Reflect.set()

The static Reflect.set() method works like setting a property on an object.

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Syntax

Reflect.set(target, propertyKey, value)
Reflect.set(target, propertyKey, value, receiver)

Parameters

target

The target object on which to set the property.

propertyKey

The name of the property to set.

value

The value to set.

receiver Optional

The value of this provided for the call to the setter for propertyKey on target. If provided and target does not have a setter for propertyKey, the property will be set on receiver instead.

Return value

A Boolean indicating whether or not setting the property was successful.

Exceptions

A TypeError, if target is not an Object.

Description

The Reflect.set method allows you to set a property on an object. It does property assignment and is like the property accessor syntax as a function.

Examples

Using Reflect.set()

// Object
let obj = {};
Reflect.set(obj, "prop", "value"); // true
obj.prop; // "value"

// Array
let arr = ["duck", "duck", "duck"];
Reflect.set(arr, 2, "goose"); // true
arr[2]; // "goose"

// It can truncate an array.
Reflect.set(arr, "length", 1); // true
arr; // ["duck"]

// With just one argument, propertyKey and value are "undefined".
let obj = {};
Reflect.set(obj); // true
Reflect.getOwnPropertyDescriptor(obj, "undefined");
// { value: undefined, writable: true, enumerable: true, configurable: true }

Different target and receiver

When the target and receiver are different, Reflect.set will use the property descriptor of target (to find the setter or determine if the property is writable), but set the property on receiver.

const target = {};
const receiver = {};
Reflect.set(target, "a", 2, receiver); // true
// target is {}; receiver is { a: 2 }

const target = { a: 1 };
const receiver = {};
Reflect.set(target, "a", 2, receiver); // true
// target is { a: 1 }; receiver is { a: 2 }

const target = {
  set a(v) {
    this.b = v;
  },
};
const receiver = {};
Reflect.set(target, "a", 2, receiver); // true
// target is { a: [Setter] }; receiver is { b: 2 }

Specifications

Specification
ECMAScript Language Specification
# sec-reflect.set

Browser compatibility

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See also