JS: Object.create

By Xah Lee. Date: . Last updated: .

Object.create

The most general way to create a object. It lets you specify its parent object, and also specify the new object's properties, and each property's attributes.

Object.create(xParent)

Return a new empty object such that its parent is xParent.

xParent is null, it creates a object without parent.

const xdad = { dog: 7 };

// create xson, with parent xdad
const xson = Object.create(xdad);

// xson's prototype is xdad
console.assert(Reflect.getPrototypeOf(xson) === xdad);

object with no parent

// create a object with no parent
const xx = Object.create(null);
console.log(xx);
// [Object: null prototype] {}

console.log(
 Reflect.getPrototypeOf(xx),
);
// null
Object.create(xParent, {k1:descriptor_1, k2:descriptor_2, etc})

Return a new object x such that x's parent is xParent and x has specified properties and attributes.

descriptor_n are Property Descriptor.

// create a object with specific parent, properties, and property attributes

const xdad = { car: 1 };

const xson = Object.create(
 xdad,
 {
  "toy": {
   value: 2,
   writable: true,
   enumerable: true,
   configurable: true,
  },
 },
);

// property car is from object xdad
console.assert(xson.car === 1);

console.assert(xson.toy === 2);

Property attributes

The Property Attributes of objects created by of Object.create , is all false, by default.

Example. create object with getter and setter

// define getter and setter properties using Object.create

const jj = Object.create(
 Object.prototype,
 {
  "dog": {
   get: function () {
    console.log("getter called");
   },
  },
  "cat": {
   set: function (x) {
    console.log("setter called with arg " + x);
   },
  },
 },
);

jj.dog;
// prints
// getter called

jj.cat = 3;
// prints
// setter called with arg 3

Example. use object.create to emulate constructor