Typescript: keyof type issue

Question

For example, if I have this User model:

export interface User {
  firstName: string;
  lastName: string;
  age: number;
  password: string;
  id: number;
}

and try to run this code:

let user = {
  firstName: 'string',
  lastName: 'string',
  age: 24,
  password: 'string',
  id: 0
}

let keys: keyof User[] = Object.keys(user) as keyof User[]; // this DOES NOT WORK

// keys: UserKeys[] = Object.keys(user) as UserKeys[];  // this works 

type UserKeys = keyof User;

I am getting this error:

Conversion of type `string[]` to type `number | keyof User[]` may be a mistake because neither type sufficiently overlaps with the other. If this was intentional, convert the expression to 'unknown' first.
  Type `string[]` is not comparable to type `"includes"`

Here is an example that reproduces the problem.

Any help will be appreciated, thanks.

UPDATE: Found a great article connected with this issue.

Hello, if it is possible to create a live example of the problem that you can link to (for example, on sqlfiddle.com or jsbin.com) then do so - but also copy the code into the question itself. Not everyone can access external sites, and the links may break over time. Use Stack Snippets to make a live demo of inline JavaScript / HTML / CSS. source: stackoverflow.com/help/how-to-ask Thanks ! — Clément Baconnier
– Clément Baconnier, Commented Apr 24, 2021 at 20:48

windowsill · Accepted Answer · 2021-04-24 20:47:36Z

2

let keys: (keyof User)[] = Object.keys(this.user) as (keyof User)[];

The problem is that keyof User[] is different than UserKeys[]. Though it's the same as (keyof User)[]

answered Apr 24, 2021 at 20:47

windowsill

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1 Comment

Ashot Aleqsanyan Over a year ago

the problem was that, the keyof User[] is trying to get the keys of User Array, not the keys of User object. that's why the () make the work correct, thank you very much

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