TypeScript type that specifically mandates the properties of an object

Question

TypeScript type that specifically mandates the properties of an object

Let's consider the following scenario:

const myObj = { foo: 'cat', bar: 'dog', baz: 'bird' } as const;

type MyValue = 'fish' | 'bear' | 'cow';

const myValueMap: Record<string, MyValue> = {
  [myObj.foo]: 'fish',
  [myObj.bar]: 'cow',
} as const;

Since myValueMap is defined as an object with indefinite string keys, there is a lack of type-checking on the specific keys of the object (cat and dog). I could eliminate the explicit declaration entirely, but that would mean not ensuring that the values are MyValues. (In my actual project, MyValue consists of numerous constant strings).

Is there a way, without resorting to a wrapper function, to guarantee that the values are MyValues while preserving the type-checking property?

TS Playground

typescript

Answer 1

Answer №1

Enhance the code by incorporating additional generics -

const myValueMap: Record<myObj[keyof myObj], MyValue> = {
  [myObj.foo]: 'fish',
  [myObj.bar]: 'cow',
};

Answer 2

Enhance the code by incorporating additional generics -

const myValueMap: Record<myObj[keyof myObj], MyValue> = {
  [myObj.foo]: 'fish',
  [myObj.bar]: 'cow',
};

Answer 3

Answer №2

Here is a code snippet that demonstrates how to achieve the desired outcome:

const animals = { cat: 'meow', dog: 'woof', bird: 'tweet' } as const;

type AnimalSounds = 'growl' | 'bark' | 'chirp';

const animalSound = animals["" as keyof typeof animals];

const soundMap: Partial<Record<typeof animalSound, AnimalSounds>> = {
  [animals.cat]: 'growl',
  [animals.dog]: 'bark',
} as const;

Answer 4

Here is a code snippet that demonstrates how to achieve the desired outcome:

const animals = { cat: 'meow', dog: 'woof', bird: 'tweet' } as const;

type AnimalSounds = 'growl' | 'bark' | 'chirp';

const animalSound = animals["" as keyof typeof animals];

const soundMap: Partial<Record<typeof animalSound, AnimalSounds>> = {
  [animals.cat]: 'growl',
  [animals.dog]: 'bark',
} as const;

TypeScript type that specifically mandates the properties of an object

Answer №1

Answer №2

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