Pickbytype

挑战

From T, pick a set of properties whose type are assignable to U.

For Example

type OnlyBoolean = PickByType<
  {
    name: string;
    count: number;
    isReadonly: boolean;
    isEnable: boolean;
  },
  boolean
>; // { isReadonly: boolean; isEnable: boolean; }

解答

这道题可以通过把映射类型和条件类型结合起来来解决。我们可以通过遍历 T 的所有属性，然后检查属性的类型是否可以赋值给 U 来实现。

type PickByType<T, U> = {
  [K in keyof T as T[K] extends U ? K : never]: T[K];
};