ts note

[chiyan-lin]

ts 实现一个不可 new 的工厂

class Singleton {
  private static instance: Singleton;
  private constructor() {
    // ..
  }

  public static getInstance() {
    if (!Singleton.instance) {
      Singleton.instance = new Singleton();
    }

    return Singleton.instance;
  }

  someMethod() {}
}

// 类“Singleton”的构造函数是私有的，仅可在类声明中访问。
let someThing = new Singleton(); 

let instacne = Singleton.getInstance(); 

[chiyan-lin]

ts keyof

type Todo = {
  id: number;
  text: string;
  done: boolean;
}

const todo: Todo = {
  id: 1,
  text: "TypeScript keyof",
  done: false
}

function prop<T extends object, K extends keyof T>(obj: T, key: K) {
  return obj[key];
}

const id = prop(todo, "id"); // const id: number
const text = prop(todo, "text"); // const text: string
const done = prop(todo, "done"); // const done: boolean

[chiyan-lin]

添加属性的混合例子

type Constructor<T = {}> = new (...args: any[]) => T;

// 添加属性的混合例子
function TimesTamped<TBase extends Constructor>(Base: TBase) {
  return class extends Base {
    timestamp = Date.now();
  };
}

// 添加属性和方法的混合例子
function Activatable<TBase extends Constructor>(Base: TBase) {
  return class extends Base {
    isActivated = false;

    activate() {
      this.isActivated = true;
    }

    deactivate() {
      this.isActivated = false;
    }
  };
}

class User {
  name = '';
}

// 添加 TimesTamped 的 User
const TimestampedUser = TimesTamped(User);

// Tina TimesTamped 和 Activatable 的类
const TimestampedActivatableUser = TimesTamped(Activatable(User));

// 使用组合类

const timestampedUserExample = new TimestampedUser();
console.log(timestampedUserExample.timestamp);

const timestampedActivatableUserExample = new TimestampedActivatableUser();
console.log(timestampedActivatableUserExample.timestamp);
console.log(timestampedActivatableUserExample.isActivated);