typescripttypescript-typingstypescript-genericstypescript-utility

Utility types that converts each member of an object type

How can I create a type Promises<T> where T is an object, such that the new type has all the same members of T, and for each member of type T[key] we have instead the type Promise<T[key]>?

Solution

  • You can do this with a mapped type:

    type Promises<T extends object> = { [K in keyof T]: Promise<T[K]> }

    Let's test it out:

    interface Foo {
  a: string;
  b: number;
  c: boolean;
}

type PromisesFoo = Promises<Foo>;
/* type PromisesFoo = {
    a: Promise<string>;
    b: Promise<number>;
    c: Promise<boolean>;
} */

    Looks good.

    Playground link to code