ts 工具类型

前言

ts 提供了很多工具类型。

工具类型

Partial 部分类型

interface User {
  id: number;
  name: string;
}
const user: User = {
  name: "test"
} // 会报错，需要用 Partial 工具包起来，表示是 User 类型的一部分
const user: Partial<User> = {
  name: "test"
}

Required 必填类型

interface User {
  id?: number;
  name: string;
}
const user: Required<User> = {
  name: "test"
} // 报错，要求必须有 id 
// Property 'id' is missing in type '{ name: string; }' but required in type 'Required<User>'.

Readonly 只读类型

interface User {
  id: number;
  name: string;
}
const user: Readonly<User> = {
  id: 123,
  name: "test"
}
user.id = 456; // 报错 Cannot assign to 'id' because it is a read-only property

Pick 获取 key 类型（和对象有关）

interface User {
  id: number;
  name: string;
  age: number;
}
type God = Pick<User, 'id' | 'name'>
// 等同于
// type God = {
//     id: number;
//     name: string;
// }

Omit 排除 key 类型（和对象有关）

和 pick 相反的操作

interface User {
  id: number;
  name: string;
  age: number;
}
type God = Omit<User, 'age'>
// 等同于
// type God = {
//     id: number;
//     name: string;
// }

Exclude 排除值类型

type Direction = '东' | '南' | '西' | '北';
type Direction2 = Exclude<Direction, '东'>;
// 等同于
// type Direction2 = "南" | "西" | "北"

Extract 提取值类型

和 exclude 相反

type Direction = '东' | '南' | '西' | '北';
type Direction2 = Extract<Direction, '南' | '西' | '北'>
// 等同于
// type Direction2 = "南" | "西" | "北"

ReturnType 返回值类型

function f(a: number, b: number) {
  return a + b;
}
type A = ReturnType<typeof f>;
// type A = number

Record 类型

type A = Record<string, number>;
// 等同于
// type A = {
//     [x: string]: number;
// }