TS create keys of new type from array of strings

Question

I simply want to maintain an array of values that dynamically scales the type definition of FiatExchangeRates.

Any idea how to solve this?

const currencies = ['eur', 'usd', 'gbp', 'chf'] as const;

type FiatExchangeRates = {
    // ... how to get the following?
    // eur: number,
    // usd: number,
    // gbp: number,
    // chf: number,
}

const fiatExchangeRates: FiatExchangeRates = {
  eur: 1.11,
  usd: 1.12,
  gbp: 1.13,
  chf: 1.14,
};

const a = fiatExchangeRates.eur;

score 3 · Accepted Answer · answered Oct 24 '21 at 11:01

3

You can extract tuple member type and use mapped type to create a desired one:

type FiatExchangeRates = { [K in (typeof currencies)[number]] : number }

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answered Oct 24 '21 at 11:01

Aleksey L.

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wow thank you for the quick response :) – user15255249 Oct 24 '21 at 11:04
Do you know to also convert the `currencies` const into a new type like this: `type Currency = 'eur' | 'usd' | 'gbp' | 'chf'` – user15255249 Oct 24 '21 at 11:07
`type Currency = (typeof currencies)[number]` already part of the answer . `type FiatExchangeRates = { [C in Currency]: number }` – Aleksey L. Oct 24 '21 at 11:09
coooool :) thanks – user15255249 Oct 24 '21 at 11:10

TS create keys of new type from array of strings

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