다양한 상황에서 사용되는 싱글턴

function singleton<Value>(name: string, value: () => Value): Value {
  const yolo = global as any;
  yolo.__singleton ??= {};
  yolo.__singleton[name] ??= value();
  return yolo.__singleton[name];
}

declare global {
  interface Global {
    __singleton?: Map<string, unknown>;
  }
}

interface Global {
  __singleton?: Map<string, unknown>;
}

export function singleton<Value>(name: string, value: () => Value): Value {
  const thusly = globalThis as Global;
  thusly.__singleton ??= new Map();
  if (!thusly.__singleton.has(name)) {
    thusly.__singleton.set(name, value());
  }
  return thusly.__singleton.get(name) as Value;
}

class Car {
  constructor(make, model, year) {
    this.make = make;
    this.model = model;
    this.year = year;
    this.speed = 0;
  }

  accelerate(amount) {
    this.speed += amount;
  }

  brake(amount) {
    this.speed = Math.max(0, this.speed - amount);
  }
}

const car1 = new Car("KIA", "K7", 2022);
const car2 = new Car("HYNDAI", "Sonata", 2023);

class DB {
  constructor() {
    this.table = {};
  }

  set(name, value) {
    this.table[name] = value;
  }

  get(name) {
    return this.table[name];
  }
}

const db1 = new DB();
db1.set("sunub", { country: "Korea" });

const db2 = new DB();
const { country } = db2.get("sunub");

class Singleton {
  static #instance = null;
  constructor() {}

  getInstance() {
    if (Singleton.#instance == null) {
      Singleton.#instance = new Singleton();
    }
    return Singleton.#instance;
  }
}

const Singleton = (() => {
  const constructorKey = Symbol("constructor");
  return class {
    static #instance = null;

    constructor(key) {
      if (key !== constructorKey) {
        throw new Error("Private constructor, use getInstance() method.");
      }
    }

    static getInstance() {
      if (!Singleton.#instance) {
        Singleton.#instance = new Singleton(constructorKey);
      }
      return Singleton.#instance;
    }
  };
})();

class Singleton {
  private static instance: Singleton | null = null;
  private constructor() {}

  public static getInstance(): Singleton {
    if (Singleton.instance === null) {
      Singleton.instance = new Singleton();
    }
    return Singleton.instance;
  }
}