Is it possible to infer string to number in TypeScript?

Asked Dec 22 '20 at 14:50

Active Dec 22 '20 at 22:09

Viewed 145 times

Let's say I have next type:

type NumberToString<T extends number> = `${T}`;

Is it possible to infer NumberToString in other direction ?

    type NumberToString<T extends number> = `${T}`;
    type StringToNumber<T extends NumberToString<number>> = T extends `${infer R}` ? R extends number ? R : never : never;
    type Result = StringToNumber<'5'>

type Result = StringToNumber<'5'> // never, but I'd like to be 5

I'm interested in solution without any mapping. It should be completely generic and it should be literal typescript type, not value

I mean, next code should work

type Result = StringToNumber<'9525'> // 9525 as number

I'd willing to bet that it is impossible

edited Dec 22 '20 at 22:09

asked Dec 22 '20 at 14:50

captain-yossarian from Ukraine

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What's wrong with `parseInt`? Trying to do this at compile-time seems... error prone. – Jared Smith Dec 22 '20 at 14:53
@JaredSmith I'm interested only in literal types. Sorry, I was not clear enough – captain-yossarian from Ukraine Dec 22 '20 at 14:55
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Ah ok, you don't want type number, you want *type 5*. Got it. – Jared Smith Dec 22 '20 at 14:56
@JaredSmith exactly, I want 5 as a literal type – captain-yossarian from Ukraine Dec 22 '20 at 14:57
Workaround https://stackoverflow.com/questions/69089549/typescript-template-literal-type-how-to-infer-numeric-type/69090186#69090186 – captain-yossarian from Ukraine Sep 08 '21 at 15:06
Marking this question as a duplicate of [TypeScript Template Literal Type - how to infer numeric type?](https://stackoverflow.com/questions/69089549/typescript-template-literal-type-how-to-infer-numeric-type), which you'd linked @captain-yossarian: That question is newer, but it has your accepted answer, so it seems pretty reasonable to direct readers there even if this one is cleaner or more general. – Jeff Bowman Sep 22 '21 at 18:00
@Jeff Bowman. Thanks a lot, you are right. – captain-yossarian from Ukraine Sep 22 '21 at 22:00
It is doable since TS 4.8 . See [PR](https://github.com/microsoft/TypeScript/pull/48094) – captain-yossarian from Ukraine Jun 11 '22 at 10:00

Is it possible to infer string to number in TypeScript?

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