How to construct a type which is the union of value from a const array? [duplicate]

Question

I have an array:

const specialNumbers = [1, 10, 20, 50] as const; // type: readonly [1, 10, 20, 50]

I would like a type (ex: SpecialNumber) that is the union of the values in the arrays.

For example to be used as:

const getSpecialNumber = (): SpecialNumber => { // SpecialNumber = 1 | 10 | 20 | 50
  // ...
}

How to construct SpecialNumber from specialNumbers?

This question is similar to: Define a union type from an array of strings. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. — jonrsharpe
– jonrsharpe, Commented Sep 25, 2024 at 7:51
"[1, 10, 20, 50] as const; // type: readonly [2, 4, 6, 8]" - something is off there — Bergi
– Bergi, Commented Sep 25, 2024 at 7:57
@jonrsharpe, that's the answer I was looking for but it didn't appear in my search. Maybe because the question was not generic enough (the title only mention strings) — Valentin Vignal
– Valentin Vignal, Commented Sep 25, 2024 at 7:59

Valentin Vignal · Accepted Answer · 2024-09-25 07:46:57Z

1

To get the union of the values, you can do:

type SpecialNumber = (typeof specialNumbers)[number];

answered Sep 25, 2024 at 7:46

Valentin Vignal

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