How to assign the result of an object breakdown to a variable that contains all unstructured fields?

Question

Given an object x:

const x = { a: 1, b: 2, c: 3 };

and a breakdown:

const { a, b } = x;

How do I save these unstructured fields in an object that brings them together without having to:

const y = {a, b};

---

I tried to make

const y = { a, b } = x;

but y becomes a reference to x, that is to say, x === y results in true

Is it possible to do this at ES6? I found nothing about it in the documentation of Mozilla

const x = { a: new Date(), b: ['foo', 'bar'], c: { name: 'John' } };
const y = { a, b } = x;

console.log(x === y);

Answer 1

You cannot do this. By the very name of the resource - de-structuring -, you are removing, unstructured an object. There is no way to use a "disruptor" as a tool to build other objects.

What you can do is create a function that does that for you, as a pick:

function pick(obj, props) {
  const newObj = {};
  for (const prop of props) newObj[prop] = obj[prop];
  return newObj;
}

const obj = { a: 1, b: 2, c: 3 };
console.log(pick(obj, ['a', 'c']));

It would be very interesting to have a language syntax to solve these points that are important to maintain the quality of a code and facilitate maintenance.

In this case, use Typescript or some other language. Javascript will not always guarantee you this type of security.

However, in case you are using Typescript, you can create something a little more complex that will give you the Intellisense of some editors such as Vscode:

function pick<Obj extends { [key: string]: unknown }, Props extends keyof Obj>(
  obj: Obj,
  props: Array<Props>
): { [key in Props]: Obj[key] } {
  const newObj: Pick<Obj, Props> = {} as Pick<Obj, Props>;
  for (const prop of props) newObj[prop] = obj[prop];
  return newObj;
}

const obj = { a: 1, b: 2, c: 3 };
const result = pick(obj, ['a', 'c']);
console.log(result);

See working on Typescript playground.

Or you can use libraries that already exist, like the function pick, of the Lodash, which also offers this Intellisense if you are using Typescript.

Answer 2

Yes it is possible to do this in SE6.
It is an exclusion selection that combines the dismantling with a parameter Rest.

The original object will remain unchanged while the resulting object will be created with the properties of the original except those that have been unstructured.

const x = { a: new Date(), b: ['foo', 'bar'], c: { name: 'John' } };

//Enumere a as propriedades não quer de x
//No parâmetro rest restará o objeto com o que lhe é necessário. 
const {c, ...y} = x;

console.log(y);
console.log(x); // x permanece inalterado.