Object.Freeze Javascript

Question

How can I give an Object.Freeze on just one object?

Here's the example below where I create a, I replicate a in b, freeze the b, and try to re-assign a value to a. But it is no longer possible. Why? How do I do freeze on just one object?

Thank you!

let a = { "teste" : [1,2,3] }

// I want 'b' freezed
const b = a;
Object.freeze(b);

a.teste = [4,5,6]

console.log(a)

Your code here only involves one object. If you freeze it, it will be frozen. — JLRishe, Nov 27 '17 at 13:59

score 6 · Accepted Answer · answered Nov 27 '17 at 13:57

6

I believe you're misunderstanding the concept of references in javascript. Objects are referenced in javascript, so when you do

const b = a;

basically you are assigning b a value of the reference a, in order to get your code to work, and actually "replicate" like you intend, you need to clone the object not pass a reference.

You can use Object.assign({}, ...) to clone an object into a new one. (notice that its not deep cloning but it should get you going)

let a = { "teste" : [1,2,3] }

// I want 'b' freezed
const b = Object.assign({}, a);
Object.freeze(b);

a.teste = [4,5,6]

console.log(a)

answered Nov 27 '17 at 13:57

Bamieh

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Nice answer. You can also use spread operator for this `const b = {...a};` – Bohdan Khodakivskyi Nov 27 '17 at 13:59
true! thanks for highlighting that – Bamieh Nov 27 '17 at 14:01
3

Note that object spread is currently a [Stage 3 proposal](https://github.com/tc39/proposal-object-rest-spread), and not yet part of any ECMAScript standard. – Kara Brightwell Nov 27 '17 at 14:02
1

Thanks a looooot man, you save my life!!! – Johnson Nov 27 '17 at 14:09

score 1 · Answer 2 · answered Nov 27 '17 at 14:00

Objects in Javascript are passed by reference, so in your example, the variables a and b refer to the same object. Object.freeze works on the object itself, not the reference, so there's no difference whether you refer to it using a or b. This is the same as if you'd just set a property:

let a = { "test" : [1,2,3] }
const b = a;
b.test = [4,5,6]
console.log(a)

If you want to freeze or modify b without affecting a, you'll need to clone it first. One way of doing this is using Object.assign:

let a = { "test" : [1,2,3] }

const b = Object.assign({}, a);
Object.freeze(b);
a.test = [4,5,6]

console.log(a)

This works by copying all of a's properties to an empty object, then assigning that to b.

Got it ! Thanks a loot man :) – Johnson Nov 27 '17 at 14:11 — Johnson, Nov 27 '17 at 14:11

Object.Freeze Javascript

2 Answers2