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