TS tips

Add dynamic key to unions

export type Entity = 
 | {
     type: "user"
}| {
     type: "post"
}| {
     type: "comment"
};
  

type EntityWithId = | {
     type: "user",
     userId: string
}| {
     type: "post",
    postId: string
}| {
     type: "comment",
    commentId: string
};

const result: EntityWithId = {
    type: "user",
    userId: "1qaz"
}


// Add dynamic keys to union types  

type NewEntityWithId = {
    [EntityType in Entity["type"]]: {
        type: EntityType
    } & Record<`${EntityType}Id`, string>
}[Entity["type"]]

// const b: NewEntityWithId = {
//     user: {
//         type: "user"
//     },
//     post: {
//          type: "post"
//     },
//     comment: {
//          type: "comment"
//     }
// }

const b: NewEntityWithId = {
    type: "post",
    postId: "adfsd"
}

console.log(b)

object type to unions

// object type to unions 

export const fruitcounts = {
    banana: 3,
    apple: 4,
    grapes:40,
    jack:4
}

type singleFruitCount = 
    | {
        apple: number
    }
    | {
        banana: number
    }| {
        grapes: number
    };

type FruitCounts = typeof fruitcounts; 

type NewSingleFruitCount = {
    [K in keyof FruitCounts]: {
       [K2 in K]: number
    }
}[keyof FruitCounts]

const singleFruitCount: NewSingleFruitCount = {
   apple: 2
}

console.log(singleFruitCount)