程序类型

此类型是ts内部定义的

Record

定义：快速创建一个对象类型，接受两个参数，一个指定对象类型的key一个指定val

/**
 * Construct a type with a set of properties K of type T
 */
type Record<K extends keyof any, T> = {
    [P in K]: T;
};

举例

type Coord = Record<'x' | 'y', number>;

// 等同于
type Coord = {
  x: number;
  y: number;
}

Partial

定义：将类型定义的所有属性设置为可选

/**
 * Make all properties in T optional
 */
type Partial<T> = {
    [P in keyof T]?: T[P];
};

举例

type Coord = Partial<Record<'x' | 'y', number>>;

// 等同于
type Coord = {
  x?: number;
  y?: number;
}

Readonly

定义：设置类型里的属性为可读

/**
 * Make all properties in T readonly
 */
type Readonly<T> = {
    readonly [P in keyof T]: T[P];
};

例子

type Coord = Readonly<Record<'x' | 'y', number>>;

// 等同于
type Coord = {
    readonly x: number;
    readonly y: number;
}

Pick

定义：选出一些属性，组合成新的类型定义

/**
 * From T, pick a set of properties whose keys are in the union K
 */
type Pick<T, K extends keyof T> = {
    [P in K]: T[P];
};

🌰

type Coord = Record<'x' | 'y', number>;
type CoordX = Pick<Coord, 'x'>;

// 等用于
type CoordX = {
  x: number;
}