TS: How to extract keys from an interface and create type union

Question

I'm sorry for the bad title, I'm not sure how to describe the situation and maybe that's why I still haven't found the solution

i have an interface

interface Fields {
  name: string
  age: number
}

and I would like to extract the keys to create a type, for example

type FieldList = ?

// expected result
// type FieldList = 'name' | 'age'

and at another time I would like to use the extracted type to create an array

const list: FieldList = ['name', 'age']

Does this answer your question? [Get keys of a Typescript interface as array of strings](https://stackoverflow.com/questions/43909566/get-keys-of-a-typescript-interface-as-array-of-strings) — pilchard, May 28 '21 at 20:59
You need union type from another Interface `type FieldsKeys = keyof Fields;` `type FieldList = FieldsKeys[];` Check [this](https://www.typescriptlang.org/play?#code/C4TwDgpgBAYglhANgEwM5QLxQN4FgBQUUAdgIYC2EAXFKsAE5zEDmBRpz1JAruQEYR6BAL4ECoSLAQoAMnDqYoACgDWEEAHsAZlKRoAlAG0AugQD0ZqBOjw9chVgDkZSo6gAfKI44RHY-ADGGsQKiPLANLay4YqGAEQuEHEANFBxPilpqBqUwAAWTMxxpvgEQA) — Akhil, May 28 '21 at 21:06

rsmeral · Accepted Answer · 2021-05-28T21:05:25.650

0

I see two questions (or perhaps three).

How to get the keys of a type?

type FieldList = keyof Fields;

FieldList is now a string literal union – 'name' | 'age';

That's not possible – you can't "materialize" a type into a value.

That's just FieldList[].

const list: FieldList[] = ['name', 'age']; // ok

const badList: FieldList[] = ['address']; // error

edited May 28 '21 at 21:05

answered May 28 '21 at 20:59

rsmeral

the third answer is what i need, `get an array type which can only contain keys of another type`, but would there be any way to define this in just a single line? because this is a function parameter, [example](https://i.ibb.co/G5Gk01J/Captura-de-Tela-2021-05-28-a-s-18-14-20.png) – Yung Silva May 28 '21 at 21:15
What do you mean by _in just a single line_? From the example, I understand that you can call `removeErrors(['age', 'name'])`. – rsmeral May 28 '21 at 21:18
1

`Array` works fine, do you see anything better? – Yung Silva May 28 '21 at 21:19
thanks for all the help, [here is the final result](https://tsplay.dev/NVnxxN) – Yung Silva May 28 '21 at 21:21