Typescript dynamic typeof object key with type definitions for key values example

dynamic-object-types.ts

const GAMES = Object.freeze({
  CSGO: {
    skillLevel: 'good'
  },
  WOW: {
    skillLevel: 'average'
  }
});

type GameKey = keyof typeof GAMES;

function getGameInfo(key: GameKey) {
  return GAMES[key];
}

getGameInfo('CSGO');
getGameInfo('WOW');
getGameInfo('unknown') // COMPILE ERROR HERE

// ------------------------
// Same scenario, working with helper function to actually force types of the values

type GameInfo = { [key: string]: { skillLevel: 'good' | 'average' | 'bad' }}

function enforceObjectType<T extends GameInfo>(o: T) {
	return Object.freeze(o);
}

const GAMES2 = enforceObjectType({
  CSGO: {
    skillLevel: 'good',
  },
  WOW: {
    skillLevel: 'average'
  },
  DOTA: {
    // Compile error - missing property skillLevel
  }
});

type GameKey2 = keyof typeof GAMES2;

function getGameInfo2(key: GameKey2) {
  return GAMES[key];
}

getGameInfo2('WOW');
getGameInfo2('CSGO');
getGameInfo2('unknown') // COMPILE ERROR HERE

I found this solution to be solving the needs, although not entirely free of using JS to define the types:

type GameInfo = { [key: string]: { skillLevel: 'good' | 'average' | 'bad' }}

type EnforceObjectType<T> = <V extends T>(v: V) => V;
const enforceObjectType: EnforceObjectType<GameInfo> = v => v;

const GAMES2 = enforceObjectType({
  CSGO: {
    skillLevel: 'good',
  },
  WOW: {
    skillLevel: 'average'
  },
  DOTA: {
    // Compile error - missing property skillLevel
  }
});

type GameKey2 = keyof typeof GAMES2;

function getGameInfo2(key: GameKey2) {
  return GAMES2[key];
}

getGameInfo2('WOW');
getGameInfo2('CSGO');
getGameInfo2('unknown') // COMPILE ERROR HERE

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