convert object values to object keys in typescript

Question

I have the next object:

const obj1 = {
  a: 'x',
  b: 'y',
  c: 'z',
}

I want obtain type like this, automatically:

type Type = {
  x: number,
  y: number,
  z: number,
}

I have thought something like:

type Type = {[key in Object.values(obj1)]: number}

But obviously this not working.

SOLUTION

With help of @jcalz I managed to do it generic:

type ObjectKeysFromValues<
  O extends { [key: string | number]: string | number},
  V = string,
> = Record<O[keyof O], V>

And this can be used like this:

const obj2: ObjectKeysFromValues<typeof obj1> = {
  x: '1',
  y: '1',
  z: '1',
}

or

const obj2: ObjectKeysFromValues<typeof obj1, number> = {
  x: 1,
  y: 1,
  z: 1,
}

Maybe I should better the namming 😂

Does this approach meet your needs? If so I can write up an answer; if not, what am I missing? Note that your obj1 as defined is of type {a: string, b: string, c: string} so there's no way to figure out "x","y", or "z" from that; you need to change your definition of obj1 so that the compiler keeps track of string literal values (hence the as const). Also note that your example has syntax errors; please edit the question to add commas in the appropriate places. — jcalz
– jcalz, Commented Apr 24, 2022 at 17:51
That was what i was looking for, If you write the solution I will can check it — srhuevo
– srhuevo, Commented Apr 25, 2022 at 8:13

Reza Mirzapour · Accepted Answer · 2022-04-24 19:11:21Z

2

first you should add "as const" after your obj1 definition.

const obj1 = {
  a: "x",
  b: "y",
  c: "z",
} as const;

now you have 2 options to define your type.

1.using index signatures

type Type = {
    [P in typeof obj1[keyof typeof obj1]]: number
}

2.using "Record" that is a built-in utility type like this:

type Type = Record<typeof obj1[keyof typeof obj1], number>

answered Apr 24, 2022 at 18:39

Reza Mirzapour

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