consider the following typescript code:
type Data = [string, number, symbol]; // Array of types
// If I want to access 'symbol' I would do this:
type Value = Data[2]; //--> symbol
// I need to get the index of the 'symbol' which is 2
// How to create something like this:
type Index = GetIndex<Data, symbol>;
I want to know if there is a possibility to get the index of symbol type in the type 'Data'.
This solution returns the keys in string format (string "2" instead of number 2).
Given an array A and a value type T, we use a mapped type to check which keys of A have values that match T. If the type is correct, we return that key and otherwise we return never. That gives us a mapped tuple [never, never, "2"] representing matching and non-matching keys. We want just the values, not the tuple, so we add [number] at the end of our type which gives us the union of all elements in the tuple -- in this case it is just "2" as never is ignored here.
type GetIndex<A extends any[], T> = {
[K in keyof A]: A[K] extends T ? K : never;
}[number]
type Index = GetIndex<Data, symbol>; // Index is "2"
2Reply: is there a way to extract a literal number? like 2 – Eliav Louski
For transform to number you can use this utility type:
type ParseInt<T> = T extends `${infer N extends number}` ? N : never
Look to this question string to number
In this case it will look as:
type ParseInt<T> = T extends `${infer N extends number}` ? N : never
type GetIndex<A extends any[], T> = {
[K in keyof A]: A[K] extends T ? ParseInt<K> : never;
}[number]
type Index = GetIndex<Data, symbol>; // Index is 2 number
Data.indexOf("symbol")?