Revision history [back]
 | 1 | initial version |
The method for obtaining the type of a union that is nested in TypeScript is to use a conditional type that checks if the input type is a union or not. If it is a union, the type of each element in the union is recursively obtained and returned in a new union. Here is an example:
type FlattenUnion<T> = T extends infer U ? U : never;
type NestedUnion = { a: string } | { b: number } | { c: boolean };
type FlatUnion = FlattenUnion<NestedUnion>; // { a: string } | { b: number } | { c: boolean }
In this example, NestedUnion is a type that represents a union of three different object types. By applying FlattenUnion to NestedUnion, the resulting type FlatUnion is a union of the individual property types from each object type.