Object.fromEntries loses all types on the key

[hfhchan]

lib Update Request

Configuration Check

My compilation target is es2020 and my lib is ES2020.

Missing / Incorrect Definition

fromEntries<T = any>(entries: Iterable<readonly [PropertyKey, T]>): { [k: string]: T };

should be

fromEntries<K extends PropertyKey, T = any>(entries: Iterable<readonly [K, T]>): { [k in K]: T };

Sample Code

enum Period {
  M1 = '1m',
  M3 = '3m',
  M6 = '6m',
  Y1 = '1y',
  Y3 = '3y',
  Y5 = '5y',
  Y10 = '10y',
}

const list: [Period, moment.Moment][] = [
  [Period.M1, moment().subtract(1, 'month')],
  [Period.M3, moment().subtract(3, 'months')],
  [Period.M6, moment().subtract(6, 'months')],
  [Period.Y1, moment().subtract(1, 'year')],
  [Period.Y3, moment().subtract(3, 'years')],
  [Period.Y5, moment().subtract(5, 'years')],
  [Period.Y10, moment().subtract(10, 'years')],
];

const object: { [k in Period]: moment.Moment } = Object.fromEntries(list);

Returns error for object:

Type '{ [k: string]: Moment; }' is missing the following properties from type '{ "1m": Moment; "3m": Moment; "6m": Moment; "1y": Moment; "3y": Moment; "5y": Moment; "10y": Moment; }': "1m", "3m", "6m", "1y", and 3 more.ts(2740)

Documentation Link

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries

Notes

I've read the soundness issues discussion on Object.keys(), but I'm not seeing how that should/would apply to Object.fromEntries().

Say if I am passing a [A, B][] into Object.fromEntries() where A is union of a class C and another enum D, I am going to get C.toString() | D. I am already hitting fromEntries(entries: Iterable<readonly any[]>): any; instead.

[hfhchan]

See also: #37457 (comment)

I just noted that this doesn't work because it's possible to omit a particular row in list, but the resulting type for Object.fromEntries() would generate an object that has all possible Periods as keys.

Apparently

fromEntries<K extends PropertyKey, T = any>(entries: Iterable<readonly [K, T]>): { [k: K]: T };

doesn't work either

[hfhchan]

Essentially a duplicate of #35745 but that issue has been closed without resolution.

[RyanCavanaugh]

It wouldn't be correct to do this, because the type of an array tells you want might be in it, not what is in it. For example, list could be entirely empty, which would make object's value be { }, despite the type of object saying that it had a M1 property.

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[lbfalvy]

Why not type it as fromEntries<K, V>(entries: [K, V][]): {[k: K]?: V}?