5153 - IndexOf

[veralex]

5153 - IndexOf

by Pineapple (@pineapple0919) #medium #array

Question

Implement the type version of Array.indexOf, indexOf<T, U> takes an Array T, any U and returns the index of the first U in Array T.

type Res = IndexOf<[1, 2, 3], 2>; // expected to be 1
type Res1 = IndexOf<[2,6, 3,8,4,1,7, 3,9], 3>; // expected to be 2
type Res2 = IndexOf<[0, 0, 0], 2>; // expected to be -1

View on GitHub: https://tsch.js.org/5153

...

type IndexOf<T extends unknown[], U extends unknown, N extends number[] = []> = T extends [infer L, ...infer R]
  ? Equal<U, L> extends true
    ? N['length']
    : IndexOf<R, U, [1, ...N]>
  : -1