Suggestion: Object.getOwnPropertyNames and Object.keys should return type with keyof

[SimonMeskens]

The signature of Object.getOwnPropertyNames is getOwnPropertyNames(o: any): string[];

Would it be possible to get getOwnPropertyNames<T>(o: T): (keyof T)[]; instead?

The same for Object.keys: keys<T>(o: T): (keyof T)[];

If I'm correct, this doesn't cause any edge cases, but allows us to write more typesafe code. Right now, I'm forced to cast some things.

Here's a toy example:

const Suits = {
    clubs: { toString: () => '\u2663' },
    diamonds: { toString: () => '\u2666' },
    hearts: { toString: () => '\u2665' },
    spades: { toString: () => '\u2660' }
}

type Suit = keyof typeof Suits;

const Ranks = {
    ace: { valueOf: () => 1, toString: () => 'A' },
    deuce: { valueOf: () => 2, toString: () => '2' },
    three: { valueOf: () => 3, toString: () => '3' },
    four: { valueOf: () => 4, toString: () => '4' },
    five: { valueOf: () => 5, toString: () => '5' },
    six: { valueOf: () => 6, toString: () => '6' },
    seven: { valueOf: () => 7, toString: () => '7' },
    eight: { valueOf: () => 8, toString: () => '8' },
    nine: { valueOf: () => 9, toString: () => '9' },
    ten: { valueOf: () => 10, toString: () => 'T' },
    jack: { valueOf: () => 11, toString: () => 'J' },
    queen: { valueOf: () => 12, toString: () => 'Q' },
    king: { valueOf: () => 13, toString: () => 'K' }
}

type Rank = keyof typeof Ranks;

type Card<R extends Rank, S extends Suit> = { rank: R, suit: S }

let deck = Object
    .keys(Suits)
    .reduce<Card<Rank, Suit>[]>((cards, suit) =>
        cards.concat(Object
            .keys(Ranks)
            .map(rank => ({
                rank: <Rank>rank, // Should be inferred instead
                suit: <Suit>suit  // Should be inferred instead
            }))
        ),
    []);

As you can see, at the end there I'm forced to cast rank and suit, they should be inferred. If I change lib.d.ts to have the signature I suggest, it correctly infers the types there. It shouldn't cause edge cases or break code as I can't imagine there's any code that expects Object.keys to return a string that's not a key of that object.

The above code is MIT license btw, if anyone feels like using it.

[RyanCavanaugh]

See #13254, #12253, and others. Please search before logging a new issue.

[SimonMeskens]

I'm sorry, I forgot to look for closed issues as well as open issues