TS | 进阶 高级类型

Partial, Readonly, Record, Pick

先看看它们的源码定义：

/**
 * 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

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

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

Readonly

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

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

Pick

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

// 等用于
type CoordX = {
	x: number;
}

链判断运算符

1 /* */
2 a?.b;
3 // a b undefined a.b
4 a == null ? undefined : a.b;
5
6 a?.[b];
7 // a b undefined a[b] 8 a == null ? undefined : a[b];
9
10 a?.b()
11 // a b undefined a.b() a.b 12 a == null ? undefined : a.b();
13
14 a?.()
15 // a undefined a()
16 a == null ? undefined : a();