ts中（Exclude，Extract，Omit，Pick）

interface UserInfo {
  username: string
  password: string
  gender: number
}

type People = Pick<UserInfo, 'username'>

type Tome = Omit<UserInfo, 'gender'>

const tom: Tome = {
  username: 'tom',
  password: '33',
}

type Animal = {
  name: string
  count: number
}

type Other = {
  position: string
  name: string
  count: number
}

type Cat = Exclude<Other, Animal>

type MM = Extract<Other, Animal>

// unknown
let a: string = '99'

let b: number = a as unknown as number // 类型断言

function func(): Promise<string> {
  return Promise.resolve(33 + '')
}

function request(): Promise<number> {
  return Promise.resolve(33)
}

let c: number

let d: ReadonlyArray<number>

interface userA {
  username: string
  password: string
  [name: string]: any
}