Typescript中Partial, Readonly, Record, Pick

源码

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

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

/**
 * 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];
};

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

Record

以 typeof 格式快速创建一个类型，此类型包含一组指定的属性且都是必填。

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

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

Partial

将类型定义的所有属性都修改为可选。

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

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

Readonly

不管是从字面意思，还是定义上都很好理解：将所有属性定义为自读。

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

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

// 如果进行了修改，则会报错：
const c: Coord = { x: 1, y: 1 };
c.x = 2; // Error: Cannot assign to 'x' because it is a read-only property.

Pick

从类型定义的属性中，选取指定一组属性，返回一个新的类型定义。

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

// 等用于
type CoordX = {
	x: number;
}

本文章只是为了记录，转自掘金
作者：nachao
链接：https://juejin.cn/post/6844904066489778183
来源：掘金