create object from existing one using Object.create()

Question

hey after looking in mdn Object.create() MDN Im trying to duplicate their example but it doesnt work

here is what I tried and what I got

    const oTest = {a:1,b:2}
 
    const test1 = Object.create(oTest)
 
    console.log(oTest)  //{a: 1, b: 2}
    console.log(test1 ) //{}

I expected test1 to console {a: 1, b: 2}

I think it doesn't copy the object, but just creates a new Object prototype. if you log `test1.a` you should get `1` — Getter Jetter, Feb 06 '19 at 13:59
@OlivierKrull, "The Object.create() method creates a new object, using an existing object as the prototype of the newly created object." — Mulperi, Feb 06 '19 at 14:01
Possible duplicate of [What is Object.Create() doing under the hood?](https://stackoverflow.com/questions/49116846/what-is-object-create-doing-under-the-hood) — adiga, Feb 06 '19 at 14:05

score 2 · Accepted Answer · answered Feb 06 '19 at 14:05

As the comments said, the existing object is used as the prototype for the new created object. So you do not see it in a console.log (at least in Node). Try it in chrome and will this that the __proto__ has your oTest object.

If you want to copy the object properties in your new object you can const test2 = {...oTest}. It is the spread operator : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

score 0 · Answer 2 · answered Feb 06 '19 at 14:05

Object.create(o) creates an empty object. Sure, one that inherits properties from o, but that just means they are available on access and don't actually get copied into own properties. Your console only shows the own properties - but if you expand the object, it should also show the prototype chain.

const oTest = {a:1,b:2};
const test1 = Object.create(oTest);

console.log(oTest) // {a: 1, b: 2}
console.log(test1) // {}
console.log(Object.getPrototypeOf(test1) == oTest) // true
console.log(test1.a) // 1

score 0 · Answer 3 · answered Feb 06 '19 at 14:05

0

If you check it with Chrome Developer tools for example, you can see the prototype of the object and it's properties.

Or you can just console.log(test1.__proto__) to view those that way.

answered Feb 06 '19 at 14:05

Mulperi

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score 0 · Answer 4 · answered Feb 06 '19 at 14:15

0

May be you need to use Object.assign() to create a copy of existing object.

const oTest = {a:1,b:2}

const test1 = Object.assign(oTest)

console.log(oTest) //{a: 1, b: 2}

console.log(test1) //{a: 1, b: 2}

answered Feb 06 '19 at 14:15

Sandip

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create object from existing one using Object.create()

4 Answers4