[@types/lodash] mapValues always returns an object but type may be inferred as an array

[skyboyer]

AFAIK, _.mapValues always return an object:

_.mapValues(undefined, () => 1); // {}
_.mapValues([1,2,3], () => true); // { 1: true, 2: true, 3: true }
_.mapValues('abc', () => '-'); // { 1: '-', 2: '-', 3: '-' }

But @types/lodash may result in an array-type inferred:

const a = mapValues([1,2,3], () => true) // { 1: true, 2: true, 3: true }
//    ^? const a: boolean[]

Link to TS playground

Is it a gap or do I miss some cases when it will be correct?

[typescript-bot]

Thanks for the discussion about "lodash", some useful links for everyone:

• npm
• DT
• Related discussions

Pinging the DT module owners: @bczengel, @chrootsu, @aj-r, @e-cloud, @thorn0, @jtmthf, @DomiR, @WilliamChelman.

[aj-r]

Interesting. I don't see any indication that mapValues was designed to be used for arrays, but it probably doesn't hurt to account for arrays in the typings.

The best solution is probably to add a new mapValues overload at the top of the overloads list. Something like:

mapValues<T, TResult>(array: T[], callback: (value: T) => TResult): NumericDictionary<TResult>;

[aj-r]

I don't have time to implement this but I'd be happy to review a PR.