I have string arrays that I construct with const assertions then use them to create union types.
const keys = ["foo", "bar", "moo"] as const;
type keysUnion = typeof keys[number]; // type keysUnion = "foo" | "bar" | "moo"
Is there a way to make a utility type that does the same thing with having to type typeof and [number] each time? Asking because I use this pattern multiple times so would be nice to make it more succinct.
You cannot remove the typeof here, since you cannot use a value in a type. You must use the typeof that value when using the type of that value in a another type.
That said you could have a type like:
type ArrayMember<T extends readonly unknown[]> = T[number]
And use it like:
const keys = ["foo", "bar", "moo"] as const;
type KeysUnion = ArrayMember<typeof keys> // "foo" | "bar" | "moo"
type MyKey = ArrayMember<string[]> // string
It's not much shorter, but it does read more nicely than MyArrType[number].
func<T extends keyof Entity> = (entity: Pick<Entity, T>) => void. Is there a way to use ArrayMember inside the function type?
ArrayMember member all over the place, including in a function type. But, your posted example doesn't have any arrays, so I have no idea where you would use it in that. That is probably a separate question.