Typescript: Objects with a single key

Question

Consider the following (partially typed) function:

const fn = <T, ?? ...>(name: ??, value: T) => ({ [name]: value })

Is it possible to complete the typing this such that

fn("hello", someT)

would have type

{ hello: T }?

If not: Is there another approach giving a similar result?

I was thinking of something along the lines of

<K extends string, T>(name: K, value: T): { [k: K]: T} => ...

but this does not work.

Aluan Haddad · Accepted Answer · 2018-04-27 18:10:53Z

4

Yes.

Use a type parameter to capture the literal type of the key, a subtype of string, and use it to define a mapped type

const fn = <T, N extends string>(name: N, value: T) => <{[P in N]: T}>({
  [name]: value
});

Unfortunately, the type assertion is required.

const hasPOfNumber = fn('p', 52);

console.log(hasPOfNumber.p);

answered Apr 27, 2018 at 18:10

Aluan Haddad

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