Is it possible to convert string union type to number union type in TypeScript?

e.g. Given a union type A:

type A = '7' | '8' | '9'

Convert to:

type B = 7 | 8 | 9

The numbers in A can be any number, not just digits or integers.

Is it possible to convert string union type to number union type in TypeScript?

e.g. Given a union type A:

type A = '7' | '8' | '9'

Convert to:

type B = 7 | 8 | 9

The numbers in A can be any number, not just digits or integers.

• javascript
• typescript

Share Improve this question Follow edited Aug 27, 2021 at 9:40 T.J. Crowder 1.1m200200 gold badges2k2k silver badges2k2k bronze badges asked Aug 27, 2021 at 8:14 loveyunkloveyunk 37833 silver badges1313 bronze badges 1

• 1 Same question but without answer stackoverflow./questions/65410801/… – captain-yossarian from Ukraine Commented Aug 27, 2021 at 8:45

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2 Answers 2

Sorted by: Reset to default 6

This is now possible (as of typescript 4.8.4), using type inference:

type ToNumber<S> = S extends `${infer N extends number}` ? N : never

type A = "7" | "8" | "9" | "0.11" | "1.52"

type B = ToNumber<A>

This unfortunately cannot handle any other number formats, even in 5.2.0-beta (so 1.2e3, 0xff4, 0b1110 are off the table).

Playground Here

Going from string to number is not possible, as far as I know. However, how about the other way around, would that work for you? You can do this by using template literals:

type B = 7 | 8 | 9;

type A = `${B}`; 

Playground Link