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)
3 Answers
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.
2 Comments
dragonmnl
I edited the question to specify that I meant distinct values. is it possible to improve your answer based on that?
Buddhika Prasadh
in that case, you can use SET data structure which can store distinct values like List " const x = new Set<ValidValue>() " refer this javatpoint.com/typescript-set
You can make use of tuple type like this:
type ValidValue = 'X' | 'Y';
type MyType = {
arr: [ValidValue, ValidValue];
}
const obj :MyType = {
arr: ['X', 'Y'] // <--- valid
}
const obj2 :MyType = {
arr: ['X', 'Y', 'Y'] // <--- error
}
4 Comments
TKoL
Is it still valid with a single element?
Ryan Le
What did you mean by
single element? like [string,string]?TKoL
The OP said
How to enforce arr to have as max length N - if max length of the array is 2, that implies that you could have an array of length 1. [<element>]TKoL
I found this answer: stackoverflow.com/questions/65495285/… so if you need to also allow less-than-N length arrays, you could do
arr: [ValidValue?, ValidValue?];Since array is an Object in Javascript you can extend the type using the intersection (&) to ensure the length of the array:
type ValidValue = 'X' | 'Y';
type MyType = {
arr: ValidValue[] & { length: 2 };
}
This does however not prevent duplicated values in the array like ['X', 'X']
['X', 'X']acceptable or not?