在映射类型里，新类型以雷同的模式去转换旧类型的每个属性。

Partial

将每个属性转换为可选属性

type Partial<T> = {    [P in keyof T]?: T[P];}

例子：

type PersonPartial = Partial<Person>;//   ^ = type PersonPartial = {//       name?: string | undefined;//       age?: number | undefined;//   }

Readonly

将每个属性转换为只读属性

type Readonly<T> = {    readonly [P in keyof T]: T[P];}

例子：

type ReadonlyPerson = Readonly<Person>;//   ^ = type ReadonlyPerson = {//       readonly name: string;//       readonly age: number;//   }

Nullable

转换为旧类型和null的联结类型

type Nullable<T> = {   [P in keyof T]: T[P] | null }

例子：

type NullablePerson = Nullable<Person>;//   ^ = type NullablePerson = {//       name: string | null;//       age: number | null;//   }

Pick

选取一组属性指定新类型

type Pick<T, K extends keyof T> = {  [P in K]: T[P];}

例子：

interface Todo {  title: string;  description: string;  completed: boolean;}type TodoPreview = Pick<Todo, "title" | "completed">;const todo: TodoPreview = {  title: "Clean room",  completed: false,};todo;// ^ = const todo: TodoPreview

Record

创立一组属性指定新类型，罕用来申明一般Object对象

type Record<K extends keyof any, T> = {  [P in K]: T;}
Record属于非同态，实质上会创立新属性，不会拷贝属性修饰符。

例子：

interface PageInfo {  title: string;}type Page = "home" | "about" | "contact";const nav: Record<Page, PageInfo> = {  about: { title: "about" },  contact: { title: "contact" },  home: { title: "home" },};nav.about;// ^ = const nav: Record

Exclude

去除交加，返回残余的局部

type Exclude<T, U> = T extends U ? never : T

例子：

interface Props {  a?: number;  b?: string;}const obj: Props = { a: 5 };const obj2: Required<Props> = { a: 5 };Property 'b' is missing in type '{ a: number; }' but required in type 'Required<Props>'.

Omit

实用于键值对对象的Exclude，去除类型中蕴含的键值对

type Omit = Pick<T, Exclude<keyof T, K>>

例子：

interface Todo {  title: string;  description: string;  completed: boolean;}type TodoPreview = Omit<Todo, "description">;const todo: TodoPreview = {  title: "Clean room",  completed: false,};

ReturnType

获取返回值类型，个别为函数

type ReturnType<T extends (...args: any) => any>  = T extends (...args: any) => infer R ? R : any;

例子：

declare function f1(): { a: number; b: string };type T4 = ReturnType<typeof f1>;//    ^ = type T4 = {//        a: number;//        b: string;//    }

Required

将每个属性转换为必选属性

type Required<T> = {  [P in keyof T]-?: T[P]}

例子：

interface Props {  a?: number;  b?: string;}const obj: Props = { a: 5 };const obj2: Required<Props> = { a: 5 };// Property 'b' is missing in type '{ a: number; }' but required in type 'Required<Props>'.

除此以外，还有很多相似的映射类型，能够参考TypeScript: Documentation取得更具体的信息。