How to specify the max length of an array in a typescript type (with distinct alternative types)?

Issue

type ValidValue = 'X' | 'Y';

type MyType = {
   arr: ValidValue[];
}

How to enforce arr to have as max length N (2 in this case, because we have 2 valid distinct values)

Solution

Typescript has fixed size array which called as tuple you can use optional element in tuple like this

let t: [number, string?, boolean?];
t = [42, "hello", true];
t = [42, "hello"];
t = [42];

also, this answer had more details about fixed-size arrays and you can find about typescript Types in here.

Answered By - Buddhika Prasadh