TypeScript type that converts string to number

While solving a Advent of Typescript challenge, I stumbled upon a problem where I almost solved it but I had to convert a string constant to a number. Initially it seemed impossible to do it in TypeScript but eventually I found a way to do it using type template literals.

Solution

type ToNumber<T> = T extends `${infer U extends number}` ? U : never;

const input = "123" as const;
type Input = typeof input;
//    ^? type Input = "123"
type Output = ToNumber<typeof input>;
//     ^? type Output = 123

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