OOP Design & Patterns — Series 3

class Cache {
  static #inst;
  constructor() {
    if (Cache.#inst) return Cache.#inst;
    this.data = new Map();
    Cache.#inst = this;
  }
}
class SubCache extends Cache {}

const a = new Cache();
const b = new SubCache();

console.log(a === b, b instanceof SubCache, b instanceof Cache);

class MyArray extends Array {
  static get [Symbol.species]() {
    return Array;
  }
}

const m = new MyArray();
m.push(1, 2, 3);
const mapped = m.map((x) => x);

console.log(m instanceof MyArray, mapped instanceof MyArray, mapped instanceof Array);

function Legacy() {
  if (!new.target) return new Legacy();
  this.ok = true;
}

const a = Legacy();
const b = new Legacy();
console.log(a.ok, b.ok, a instanceof Legacy);

class Modern {}
try {
  Modern();
} catch (e) {
  console.log(e.constructor.name);
}