32. AppendToObject

[astak16]

题目

题目链接：AppendToObject，答题

实现 AppendToObject，往对象中添加一个属性

import type { Equal, Expect } from "@type-challenges/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
    >
  >
];

答案

方法一

type AppendToObject<T, K extends keyof any, V> = {
  [key in keyof T | K]: key extends keyof T ? T[key] : V;
};

知识点

将 T 中 key 和泛型 K 变成联合类型，然后就可以通过遍历 key 得到新对象

方法二

type IntersectionToObject<T> = { [K in keyof T]: T[K] };
type AppendToObject<T, K extends keyof any, V> = IntersectionToObject<
  T & {
    [key in K]: V;
  }
>;

方法三

type IntersectionToObject<T> = { [K in keyof T]: T[K] };
type AppendToObject<T, K extends keyof any, V> = IntersectionToObject<
  T & Record<K, V>
>;

知识点

方法二和方法三是相同的思路，把两个对象变成交叉对象，然后再将交叉对象转变成普通对象