常用类型

• string number boolean
• array
• any
  • noImplicitAny
• function
  • 参数类型注释

    function greet(name: string) {
      console.log("Hello, " + name.toUpperCase() + "!!");
    }

  • 返回类型注释

    function getFavoriteNumber(): number {
      return 26;
    }

    async function getFavoriteNumber(): Promise<number> {
      return 26;
    }

  • 匿名函数

    const names = ["Alice", "Bob", "Eve"];
     
    // Contextual typing for function - parameter s inferred to have type string
    names.forEach(function (s) {
      console.log(s.toUpperCase());
    });

• object
  • 定义对象类型

    function printCoord(pt: { x: number; y: number }) {
      console.log("The coordinate's x value is " + pt.x);
      console.log("The coordinate's y value is " + pt.y);
    }

  • 可选属性

    function printName(obj: { first: string; last?: string }) {
      // ...
    }

• 联合类型
  • 定义联合类型

      function printId(id: number | string) {
      console.log("Your ID is: " + id);
    }

  • 使用联合类型

    function printId(id: number | string) {
      if (typeof id === "string") {
        // In this branch, id is of type 'string'
        console.log(id.toUpperCase());
      } else {
        // Here, id is of type 'number'
        console.log(id);
      }
    }

• type 类型别名

  type Point = {
    x: number;
    y:number;
  }

  type ID = number | string;

• interface

  interface Point {
    x: number;
    y: number;
  }

• 类型断言

  const myCanvas = document.getElementById("main_canvas") as HTMLCanvasElement;

  const a = expr as any as T;

• 文字类型

  type POSITION = 'left'|'right';
  declare function handleRequest(url: string, method: "GET" | "POST"): void;

• null 和undefined
  • strictNullChecks
  • 非空断言

    function liveDangerously(x?: number | null) {
      // No error
      console.log(x!.toFixed());
    }

• enum 枚举

不常用类型

• bigint
• symbol