Jun 22, 2022
1 min read
Typescript Odd Number Type
Most people: No, you cannot create an odd number type with Typescript
Meanwhile me:
type OddNumber<
X extends number,
Y extends unknown[] = [1],
Z extends number = never
> = Y[‘length’] extends X
? Z | Y[‘length’]
: OddNumber<X, [1, 1, …Y], Z | Y[‘length’]>type a = OddNumber<1> // 1
type b = OddNumber< 3 > // 1 | 3
type c = OddNumber<5> // 1 | 3 | 5
type d = OddNumber<7> // 1 | 3 | 5 | 7
with some limitations, the input must an odd number, and cannot exceed 1999 (maximum depth of typescript recursion is only 1000)
you can do even number type using similar logic
