The Reflect.set()
static method is like the property accessor and assignment syntax, but as a function.
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
- : The value of
this
provided for the call to the setter forpropertyKey
ontarget
. If provided andtarget
does not have a setter forpropertyKey
, the property will be set onreceiver
instead.
- : The value of
Return value
A Boolean indicating whether or not setting the property was successful.
Exceptions
- TypeError
- : Thrown if
target
is not an object.
- : Thrown if
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 <span class="selflink">Set</span>
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 }