1. Awaited #

表示一个 Promise 的 resolve 值类型，可以递归的执行拆箱

type A = Awaited<Promise<string>> // type A = string
type B = Awaited<Promise<Promise<number>>> // type B = number
type C = Awaited<boolean | Promise<number>> // type C = boolean | number

2. Partial #

返回一个表示给定类型的所有子集可选的类型

interface Todo {
  title: string
  description: string
}

type P = Partial<Todo>

/**
  type P = {
    title?: string | undefined
    description?: string | undefined
  }
*/

3. Required #

跟 Partial 相反， 可选变必选

interface Props {
  a?: number
  b?: string
}

const obj2: Required<Props> = { a: 5 }  // no pass

//Property 'b' is missing in type '{ a: number; }' but required in type 'Required<Props>'.

const obj2: Required<Props> = { a: 5， b: '123' } // pass

4. Readonly #

构造一个类型，类型的所有属性都设置为只读，这意味着无法重新分配构造类型的属性。

interface Todo {
  title: string
}

const todo: Readonly<Todo> = {
  title: 'Delete inactive users',
}

todo.title = 'Hello' // no pass
// Cannot assign to 'title' because it is a read-only property.

5. Record<T,K> #

构建一个 object type, 其 key 为 T， value 为 K。可用于将一个类型的属性映射到另一个类型

interface CatInfo {
  age: number
  breed: string
}

type CatName = 'miffy' | 'boris' | 'mordred'

const cats: Record<CatName, CatInfo> = {
  miffy: { age: 10, breed: 'Persian' },
  boris: { age: 5, breed: 'Maine Coon' },
  mordred: { age: 16, breed: 'British Shorthair' },
}

cats.boris // const cats: Record<CatName, CatInfo>

6. Pick<T,K> #

从T中选择一组属性键K来构造类型

interface Todo {
  title: string
  description: string
  completed: boolean
}

type TodoPreview = Pick<Todo, 'title' | 'completed'>

const todo: TodoPreview = {
  title: 'Clean room',
  completed: false,
}

7. Omit<T,K> #

通过从 T 中选取所有属性，然后移除 K 来构造类型。

interface Todo {
  title: string
  description: string
  completed: boolean
  createdAt: number
}

type TodoPreview = Omit<Todo, 'description'> // type TodoPreview = { completed: boolean createdAt: number title: string }

const todo: TodoPreview = {
  title: 'Clean room',
  completed: false,
  createdAt: 1615544252770,
}

type TodoInfo = Omit<Todo, 'completed' | 'createdAt'> // // type TodoInfo = { description: string title: string }

const todoInfo: TodoInfo = {
  title: 'Pick up kids',
  description: 'Kindergarten closes at 5pm',
}

8. Exclude<UnionType, ExcludedMembers> #

通过从 UnionType 中排除可分配给 ExcludedMembers 的所有联合类型来构造类型。

type T0 = Exclude<'a' | 'b' | 'c', 'a'> // type T0 = "b" | "c"

type T1 = Exclude<'a' | 'b' | 'c', 'a' | 'b'> // type T1 = "c"

type T2 = Exclude<string | number | (() => void), Function> // type T2 = string | number

9. Extract<T, Union> #

通过从 T 中提取可分配给 Union 的所有联合类型来构造类型

type T0 = Extract<'a' | 'b' | 'c', 'a' | 'f'> // type T0 = "a"

type T1 = Extract<string | number | (() => void), Function> // type T1 = () => void

10. NonNullable #

通过从 T 中排除 null 和 undefined 来构造类型。

type T0 = NonNullable<string | number | undefined> // type T0 = string | number

type T1 = NonNullable<string[] | null | undefined> // type T1 = string[]