Reflect.construct()

Baseline

20169

Reflect.construct() new new target(...args) new.target

function func1(a, b, c) {
  this.sum = a + b + c;
}

const args = [1, 2, 3];
const object1 = new func1(...args);
const object2 = Reflect.construct(func1, args);

console.log(object2.sum);
// : 6

console.log(object1.sum);
// : 6

Reflect.construct(target, argumentsList)
Reflect.construct(target, argumentsList, newTarget)

target
argumentsList: target
newTarget: target new.target target target newTarget.prototype

target ( newTarget) target argumentsList

TypeError: target newTarget argumentsList

Reflect.construct() Reflect.construct(target, argumentsList, newTarget)

new target(...argumentsList);

new target newTarget Reflect.construct() new.target newTarget new newTarget.prototype target new.target

class A {
  constructor() {
    console.log(new.target.name);
  }
}
class B extends A {}

new B(); // "B"

Reflect.construct()

const obj = new Foo(...args);
const obj = Reflect.construct(Foo, args);

Reflect.construct() target [[Construct]]

Reflect.construct()

const d = Reflect.construct(Date, [1776, 6, 4]);
d instanceof Date; // true
d.getFullYear(); // 1776

new.target

newTarget new.target target newTarget

function OneClass() {
  console.log("OneClass executed");
  console.log(`new.target is ${new.target.name}`);
}

function OtherClass() {
  console.log("OtherClass executed");
  console.log(`new.target is ${new.target.name}`);
}

const obj1 = Reflect.construct(OneClass, []);
// :
// OneClass executed
// new.target is OneClass
console.log(obj1 instanceof OneClass); // true

const obj2 = Reflect.construct(OneClass, [], OtherClass);
// :
// OneClass executed
// new.target is OtherClass
console.log(obj2 instanceof OtherClass); // true
console.log(obj2 instanceof OneClass); // false

target newTarget target construct

function OneClass() {
  return { name: "one" };
}

function OtherClass() {
  return { name: "other" };
}

const obj1 = Reflect.construct(OneClass, [], OtherClass);
console.log(obj1.name); // 'one'
console.log(obj1 instanceof OneClass); // false
console.log(obj1 instanceof OtherClass); // false

new.target prototype prototype Object.prototype

function OneClass() {
  console.log("OneClass executed");
  console.log(`new.target is ${new.target.name}`);
}

function OtherClass() {
  console.log("OtherClass executed");
  console.log(`new.target is ${new.target.name}`);
}

OtherClass.prototype = null;

const obj = Reflect.construct(OneClass, [], OtherClass);
// :
// OneClass executed
// new.target is OtherClass
console.log(Object.getPrototypeOf(obj) === Object.prototype); // true

Reflect.construct() Object.create()

Reflect Object.create()

function OneClass() {
  this.name = "one";
}

function OtherClass() {
  this.name = "other";
}

const args = [];
const obj1 = Reflect.construct(OneClass, args, OtherClass);
const obj2 = Object.create(OtherClass.prototype);
OneClass.apply(obj2, args);

console.log(obj1.name); // 'one'
console.log(obj2.name); // 'one'

console.log(obj1 instanceof OneClass); // false
console.log(obj2 instanceof OneClass); // false

console.log(obj1 instanceof OtherClass); // true
console.log(obj2 instanceof OtherClass); // true

2 Object.create() Function.prototype.apply() new.target undefined new apply construct

Reflect.construct() new.target newTarget target

function OneClass() {
  console.log("OneClass");
  console.log(new.target);
}
function OtherClass() {
  console.log("OtherClass");
  console.log(new.target);
}

const obj1 = Reflect.construct(OneClass, args);
// :
// OneClass
// function OneClass { ... }

const obj2 = Reflect.construct(OneClass, args, OtherClass);
// :
// OneClass
// function OtherClass { ... }

const obj3 = Object.create(OtherClass.prototype);
OneClass.apply(obj3, args);
// Output:
//     OneClass
//     undefined


ECMAScript 2027 LanguageSpecification # sec-reflect.construct

MDN

MDN 2026523

GitHub

Reflect