Typescript array destructuring type

Question

How should I type following destructured array?

const [first, ...rest] = this.employee.roles;

The code above works, but project rules impose const typing.

I tried:

const first: Role;
const rest: Array<Role>;
[first, ...rest] = this.employee.roles;

but then I need to change const to let for [first, ...rest] = this.employee.roles; to work

Following code also works, but isn't it misleading?

const [first, ...rest]: Array<Role> = this.employee.roles;

since first is Role and rest is Array<Role> I'm not sure about this one.

I'd like something similar to this:

const [first, ...rest]: [first: Role, rest: Array<Role>] = this.employee.roles;

but it's not compiling.

Is there a clean way of typing this or should I just switch to

let first: Role;
let rest: Array<Role>;
[first, ...rest] = this.employee.roles;

i think your first idea is correct: const [first, ...rest]: Array<Role> = this.employee.roles; (try console logging [first, ...rest] out) — milan
– milan, Commented Mar 17, 2022 at 9:46
if this.employee.roles is already typed, the type of first and rest should be inferred correctly. if you really need to specify it, this const [first, ...rest]: Array<Role> = this.employee.roles; looks correct to me aswell — coglialoro
– coglialoro, Commented Mar 17, 2022 at 10:11

Titian Cernicova-Dragomir · Accepted Answer · 2022-03-17 10:28:27Z

2

I would just use onst [first, ...rest]: Array<Role>. If you want you can type is with tuple types, but you will have to make first optional, since there is no guarantee Role[] will contain any elements, it could be empty:


const [first, ...rest]: [first?: Role, ...rest: Array<Role>] = roles;

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answered Mar 17, 2022 at 10:28

Titian Cernicova-Dragomir

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