关于javascript:TypeScript-基础理论

基础知识

根底类型：number string boolean array object

1. enum 枚举
   接口给前端返回一盒status字段

    enum ActivityStatus {     NOT_START = 'notStart',     STARTED = 'stated' } const status = ActivityStatus.NOT_START;

2. type, interface

    // type UserInfo = {    //     name: string;    //     height?: number    // }        interface UserInfo {        name: string;        height?: number    }    const userInfo = {        name: 'cxx'    }

3. 联结类型 | (联结类型一次只能应用一种类型，而穿插类型每次都是多个合并类型)
4. 穿插类型 & (联结类型一次只能应用一种类型，而穿插类型每次都是多个合并类型)

    interface UserInfoA {        name?: string;        height?: number    }    interface UserInfoB {        width: number    }    function test (param: UserInfoA | UserInfoB){        // ...    }

5. typeof

    typeof 'a' //string

    function toArray(x: number):Array<number>{     return {x}; } type Func = typeof toArray; // (x: number) => number[]

6. keyof

    // 能够用来获取一个对象中所有的key值    interface Person{        name: string;        age: number;    }    type KPerson = keyof Person; // 'name' | 'age'

7. in 用来遍历枚举类型

    type Keys = 'a' | 'b' | 'c'; type obj = {     [key in Keys]: any; }

8. extends 继承类型

    interface TLength{     length: number } function loggingIdentity<T extends TLength>(arg: T): T{     console.log(arg.length);     return arg; } loggingIdentity(3); loggingIdentity({length: 10, value: 3});

9. Paritial
   Paritial<T> 的作用是将某个类型的属性全副变为可选项

    interface PageInfo{     title: string; } type OptionalPageInfo = Paritial<PageInfo>;

10. Required 全副变为必选项

11. Readonly 全副变为只读

     interface PageInfo{     title: string; } type ReadonlyPageInfo = Readonly<PageInfo>; const pageInfo: ReadonlyPageInfo = { title: 'cxx' }; pageInfo.title = 'ch'; // error

12. Record
    Record<K extends keyof any, T> 将K中的所有属性的值转化为T类型

     interface PageInfo{     title: string; } type Page = "home" | "about" | "contact"; const x: Record<Page, PageInfo> = {     home: {title: '111'},     about: {title: '222'},     contact: {title: '333'}, }

13. Exclude
    Exclude<T, U> 将某个类型中属于另一个的类型移除

     type T0 = Exclude<"a" | "b" |"c", "a">    // "b | "c" type T1 = Exclude<"a" | "b" |"c", "a" | "b">    // "c"

14. Extract
    Extract<T, U> 从T中提取U，大略是取交加的意思

     type T0 = Extract<"a" | "b" |"c", "a" | "f">    // "a" type T1 = Extract<string | number | (() => void), Function>    // () => void