Reflect.set()
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.set() static method is like the property accessor and assignment syntax, but as a function.
Try it
const object = {};
Reflect.set(object, "foo", 42);
console.log(object.foo);
// Expected output: 42
const array = ["duck", "duck", "duck"];
Reflect.set(array, 2, "goose");
console.log(array[2]);
// Expected output: "goose"
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.
receiverOptional-
The value of
thisprovided for the call to the setter forpropertyKeyontarget. If provided andtargetdoes not have a setter forpropertyKey, the property will be set onreceiverinstead. Defaults totarget.
Return value
A Boolean indicating whether or not setting the property was successful.
Exceptions
TypeError-
Thrown if
targetis not an object.
Description
Reflect.set() provides the reflective semantic of a property access. That is, Reflect.set(target, propertyKey, value, receiver) is semantically equivalent to:
target[propertyKey] = value;
Note that in a normal property access, target and receiver would observably be the same object.
Reflect.set() invokes the [[Set]] object internal method of target.
Examples
Using Reflect.set()
// Object
const obj = {};
Reflect.set(obj, "prop", "value"); // true
obj.prop; // "value"
// Array
const 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".
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 |
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| ECMAScript® 2027 Language Specification # sec-reflect.set |
Browser compatibility
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Legend
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