类型：

用法

• number

  let decimal: number = 6;
  let hex: number = 0xf00d;
  let big: bigint = 100n;
  

• boolean

  let isDone: boolean = false;
  

• string

  let color: string = "blue";
  color = 'red';
  

• 字面量

• 也可以使用字面量去指定变量的类型，通过字面量可以确定变量的取值范围

  let color: 'red' | 'blue' | 'black';
  let num: 1 | 2 | 3 | 4 | 5;
  

• any

  let d: any = 4;
  d = 'hello';
  d = true;
  

• unknown

  let notSure: unknown = 4;
  notSure = 'hello';
  

• void

  let unusable: void = undefined;
  function fn(): void{}
  function fn(): void {
     return undefined
  }
  

• never

  function error(message: string): never {
     throw new Error(message);
  }
  

• object（没啥用）

  let obj: object = {};
  

• array

  let list: number[] = [1, 2, 3];
  let list: Array<number> = [1, 2, 3];
  

• tuple

  let x: [string, number];
  x = ["hello", 10]; 
  

• enum

  enum Color {
     Red,   // 0
     Green, // 1
     Blue,  // 2
  }
  let c: Color = Color.Green;
  
  enum Color {
     Red = 1,  // 1
     Green,    // 2
     Blue,     // 3
  }
  let c: Color = Color.Green;
  
  enum Color {
     Red = 1,    // 1
     Green = 2,  // 2
     Blue = 4,   // 4
  }
  let c: Color = Color.Green;
  

断言

      //写法1
      let someValue: unknown = "this is a string";
      let strLength: number = (someValue as string).length;
      //写法2
      let someValue: unknown = "this is a string";
      let strLength: number = (<string>someValue).length;
      ```

接口

• 接口的作用类似于没有实际值的抽象类
• 可以用于定义对象，方法的参数/返回值，接口（使用extends关键字），类（使用implements关键字）的结构

  //对象
  interface Info {
     name: string
     age: number
     say?: () => void
  }
  
  const user: Info = {
     name: '张三',
     age: 18,
     say: () => {
        console.log(`我叫${this.name}`)
     }
  }
  //方法的参数和返回值
  interface sum {
     (a: number, b: number): number
  }
  
  const add: sum = (a, b) => {
     return a + b;
  }
  sum(1, 2)
  // 接口
  interface Person{
     name: string;
     say():void;
  }
  interface man extends Person{
     eat():void;
  }
  // 类
  interface Person{
     name: string;
     say():void;
  }
  interface Student{
     hello():void;
  }
  // 同时执行多个接口，用`,`隔开
  class Student implements Person,Student{
     constructor(public name: string) {}
     say() {
        console.log(`我叫${this.name}`);
     }
     hello() {
        console.log(`我是一个学生`);
     }
  }
  

Class （链接: link）

泛型（链接：link）