I want to take type stringUnion = "Value1"|"Value2"
and make an array from all the strings in stringUnion
so the array looks like this ["Value1","Value2"],
I want an array so I can iterate over it like this:
theArray.map((current, index)=>{
})
How do I do that?
Yes, it is possible.
// credits goes to https://stackoverflow.com/questions/50374908/transform-union-type-to-intersection-type/50375286#50375286
type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends (
k: infer I
) => void
? I
: never;
// credits goes to https://github.com/microsoft/TypeScript/issues/13298#issuecomment-468114901
type UnionToOvlds<U> = UnionToIntersection<
U extends any ? (f: U) => void : never
>;
type PopUnion<U> = UnionToOvlds<U> extends (a: infer A) => void ? A : never;
// credits goes to https://stackoverflow.com/questions/53953814/typescript-check-if-a-type-is-a-union#comment-94748994
type IsUnion<T> = [T] extends [UnionToIntersection<T>] ? false : true;
type UnionToArray<T, A extends unknown[] = []> = IsUnion<T> extends true
? UnionToArray<Exclude<T, PopUnion<T>>, [PopUnion<T>, ...A]>
: [T, ...A];
interface Person {
name: string;
age: number;
surname: string;
children: number;
}
type Result = UnionToArray<keyof Person>; // ["name", "age", "surname", "children"]
Here is an alternative way:
// credits goes to https://twitter.com/WrocTypeScript/status/1306296710407352321
type TupleUnion<U extends string, R extends any[] = []> = {
[S in U]: Exclude<U, S> extends never ? [...R, S] : TupleUnion<Exclude<U, S>, [...R, S]>;
}[U];
interface Person {
firstName: string;
lastName: string;
dob: Date;
hasCats: false;
}
type keys = TupleUnion<keyof Person>;
More explanation you can find in my blog
You can't use the stringUnion as a value in a variable (because types are not transpiled to js code).
But if this array is gonna be a constant, you can use:
const stringValues = ["value1", "value2"] as const;
type stringUnion = (typeof stringValues)[number];
Which will allow you to write the values only once.
It is not possible to create a value out of a type. So you can't convert your union type to an array. If you wish to create an array type though. You can do it in 2 ways.
type YourArrayType = StringUnion[];type YourArrayType = Array<StringUnion>;This type will create the following type: ("value1" | "value2")[] and it will only allow you to have either "value1" or "value2" in your array with this type.
