Javascript destructuring and assignment into new object

Question

Lets say I have an object:

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

Now I can destructure as follows:

let {a,b} = x;

Is it possible to assign, (in the same line as the destructuring) these into a new object, the equivalent of?:

let newObject = {a,b};

or (in pseudocode, I realise this doesn't work)

let newObject = {a,b} = x;

or would I be required to use something as lodash _.pickBy function?

let newObject = _.pickBy(x,['a','b'])

The reason I am asking is, I would like to do something like that for functions signatures:

let fun = ({a,b}) => {
    let args = {a,b}; // <---- 
}

You don't want to use this `let newObject = {a : x.a, b : x.b};` ? — Tushar Shahi, Jul 17 '21 at 17:10
@MikeM yep, i get that, but If I have lots of variables it gets tedious. — Nicholas Hamilton, Jul 17 '21 at 17:13
@TusharShahi yeah, that works but Unfortunately I really want this for function signatures where i can say declare a function `fun = ({a,b}) = {...}`, and assign all the arguments into a single object. — Nicholas Hamilton, Jul 17 '21 at 17:15
but.. how big is that argument part.. the `({a,b})` part i mean — The Bomb Squad, Jul 17 '21 at 17:19
@bombsquad, sometimes 10 or more arguments, if I am using it to create database documents. — Nicholas Hamilton, Jul 17 '21 at 17:22
I feel like you’re trying to make code more succinct, but it will just end up being confusing and less readable. Sometimes verbosity is not a bad thing — Seth Lutske, Jul 17 '21 at 18:19
@SethLutske No i'm just tired of writing many variables twice, it feels like unnecessary duplication. — Nicholas Hamilton, Jul 18 '21 at 05:43

score 1 · Answer 1 · answered Jul 17 '21 at 17:34

It seems impossible, because, while looking the same, the destructuring assignment and object syntaxes are completely different things.

let a, b;
{a,b} = x  <-- {a,b} is not an object

If you try returning the result of destructuring assignment, it will still be returning x, the full object.

const result = {a,b} = x 
// `result` is the full object

or

const result = ({a,b} = x);
// `result` is the full object

Anyway, writing such one-liners could be extremely confusing to teammates. It would raise my eyebrows during a peer review anyways :)

score 0 · Answer 2 · answered Jan 16 '23 at 09:51

I think what you need is to filter the object by key without middle variables.

Here is my solutions:

let x = {a:1,b:2,c:3}
let y = {}
;({a: y.a, b: y.b} = x)

let filterObjectByKeys = (object, keys) => Object.fromEntries(keys.map(k => [k, object[k]]))
let x = {a:1,b:2,c:3}
let y = filterObjectByKeys(x, ['a', 'b'])

Reference:

Javascript destructuring and assignment into new object

2 Answers2