TS的一些特殊示例 (持续更新)

该文章记录一些平时工作中一些特殊场景类型推导, 归纳总结一下。

定义一个不包括某些 Key 的对象

interface Options {
  name: string;
  age?: number;
}

type Valid = Record<string, any> & Partial<Record<keyof Options, never>>;

const foo: Valid = { name: 'foo' }; // error
const bar: Valid = { age: 1 };  // error
const baz: Valid = { other: 'baz' }; // okay

• TypeScript function that takes an object without certain keys

为 Object.defineProperty 添加类型推导

type InferValue<Prop extends PropertyKey, Desc> = Desc extends { get(): any; value: any }
  ? never
  : Desc extends { value: infer T }
  ? Record<Prop, T>
  : Desc extends { get(): infer T }
  ? Record<Prop, T>
  : never;

type DefineProperty<Prop extends PropertyKey, Desc extends PropertyDescriptor> = Desc extends {
  writable: any;
  set(val: any): any;
}
  ? never
  : Desc extends { writable: any; get(): any }
  ? never
  : Desc extends { writable: false }
  ? Readonly<InferValue<Prop, Desc>>
  : Desc extends { writable: true }
  ? InferValue<Prop, Desc>
  : Readonly<InferValue<Prop, Desc>>;

function defineProperty<
  Obj extends object,
  Key extends PropertyKey,
  PDesc extends PropertyDescriptor
>(obj: Obj, prop: Key, val: PDesc): asserts obj is Obj & DefineProperty<Key, PDesc> {
  Object.defineProperty(obj, prop, val);
}

const storage = {
  currentValue: 0
};

defineProperty(storage, 'maxValue', {
  value: 9001,
  writable: false
});

storage.maxValue = 100; // error

• TypeScript: Assertion signatures and Object.defineProperty