CODEWITHSUNDEEP
typescripttypescript-typingsramda.js
mtpultz
mtpultz

Reputation: 18288

Properly setting TypeScript typings for anonymous functions passed to Ramda

I'm trying to figure out what the proper typings are for the Ramda cookbook method mapKeys it won't transpile without throwing an error.

Issue

Error is on fn:

Argument of type '{}' is not assignable to parameter of type '(a: string) => string'. Type '{}' provides no match for the signature '(a: string): string'.

I can see from the typings of R.adjust that it uses generics, and I tried (a: string) => string based on the error, which should be the correct typings, and several other variations, such as (a: string) => string[].

Can someone indicate what the fn argument for the anonymous function should be to fix the typings error?

This is really easy to duplicate by just pasting the example into a TypeScript project using VSCode and installing Ramda via npm, and I include the typings for R.adjust as a reference.

Example

import * as R from 'ramda';

export const mapKeys = R.curry(
  (fn: ???, obj: { [k: string]: any } | { [k: number]: any }) =>
    R.fromPairs(
      R.map(
        R.adjust(fn, 0), // <--- Error: tried typings for `adjust`
        R.toPairs(obj)
      )
    )
);

Ramda Typings for Reference

adjust<T>(fn: (a: T) => T, index: number, list: T[]): T[];
adjust<T>(fn: (a: T) => T, index: number): (list: T[]) => T[];

Upvotes: 0

Views: 430

Answers (1)

mtpultz
mtpultz

Reputation: 18288

I posted an issue on Github for types/npm-ramda and a fix was merged into master for the next release of the Ramda typings.

Upvotes: 2

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