is there a way to limit the keys and values of an map function for an object?

[rough flicker]

lifeiscontent#6354

Playground Link

Preview:```ts
declare function map<T, U>(
value: T,
mapper: (v: T[keyof T], k: keyof T, o: T) => U
): { [Key in keyof T]: ReturnType<typeof mapper> };

const sym = Symbol('foo');

const a = { 1: "two", 3: "four", [sym]: true, "test": true };

// how can I make b have a type of {
...```

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[bold tartan]

don't think you can do that directly on the function itself

since you basically pass one key at the time (which could be typeof sym | 1 | 3 | "test") and you return it as is

so you end up with an object that looks like this Record<typeof sym | 1 | 3 | "test", typeof sym | 1 | 3 | "test">

[rough flicker]

Ascor8522#7606

Playground Link

Preview:```ts
declare function map<T, K extends keyof T, U>(value: T, mapper: (v: T[K], key: K, obj: T) => U): Record<K, U>;

const sym = Symbol('foo');

const a = {
1: "two",
3: "four",
[sym]: true,
"test": true,
};

// how can I make b have a type of {
// {
// 1: 1;
...```

You can choose specific lines to embed by selecting them before copying the link.

[bold tartan]

you can still cast the result of the function to the expected result

¯_(ツ)_/¯

@serene abyss

[serene abyss]

@bold tartan this is awesome, thank you! 🙂

@bold tartan ah, I see what you mean now.

I didn't realize you used as till now

[bold tartan]

!resolved