00527-medium-append-to-object.ts

// ============= Test Cases =============
import type { Equal, Expect } from "./test-utils";

type test1 = {
    key: "cat";
    value: "green";
};

type testExpect1 = {
    key: "cat";
    value: "green";
    home: boolean;
};

type test2 = {
    key: "dog" | undefined;
    value: "white";
    sun: true;
};

type testExpect2 = {
    key: "dog" | undefined;
    value: "white";
    sun: true;
    home: 1;
};

type test3 = {
    key: "cow";
    value: "yellow";
    sun: false;
};

type testExpect3 = {
    key: "cow";
    value: "yellow";
    sun: false;
    isMotherRussia: false | undefined;
};

type cases = [
    Expect<Equal<AppendToObject<test1, "home", boolean>, testExpect1>>,
    Expect<Equal<AppendToObject<test2, "home", 1>, testExpect2>>,
    Expect<
        Equal<
            AppendToObject<test3, "isMotherRussia", false | undefined>,
            testExpect3
        >
    >
];

// ============= Your Code Here =============
type AppendToObject<T, U extends string, V> = {
    [K in keyof T | U]: K extends keyof T ? T[K] : V;
};

type Test = AppendToObject<test3, "isMotherRussia", false | undefined>;