const memoize = (fn) => {
  const cache = new Map();
  return (...args) => {
    const key = JSON.stringify(args);
    if (cache.has(key)) return cache.get(key);
    const result = fn(...args);
    cache.set(key, result);
    return result;
  };
};

let calls = 0;
const square = memoize((x) => {
  calls++;
  return x * x;
});

console.log(square(4), square(4), square(-4), calls);

const handler = {
  get(target, prop, receiver) {
    if (!(prop in target)) {
      return `no ${String(prop)}`;
    }
    return Reflect.get(target, prop, receiver);
  },
  set(target, prop, value) {
    if (typeof value === 'number' && value < 0) {
      throw new RangeError('negative');
    }
    return Reflect.set(target, prop, value);
  }
};

const obj = new Proxy({ a: 1, b: 2 }, handler);
obj.c = 10;
console.log(obj.a, obj.c, obj.missing, obj.hasOwnProperty('a'));

let counter = 0;
const state = {
  get value() {
    counter++;
    return counter % 3 === 0 ? null : counter;
  }
};
let result;
result ??= state.value;
result ??= state.value;
result ??= state.value;
result ??= state.value;
console.log(result, counter);

const s = "JavaScript";
const str = new String(s);
console.log(str === s, str == s, typeof str, str.at(-1), s.at(-1));

const a = [] + [];
const b = [] + {};
const c = {} + [];
const d = 1 + "1" - 1;
const e = "5" - "2" + "3";
const f = [1, 2] == "1,2";
console.log(a, b, c, d, e, f);

const base = { greet() { return 'hi'; } };
const obj = Object.create(base, {
  x: { value: 1, enumerable: true },
  y: { value: 2, enumerable: false }
});
const spread = { ...obj };
const assigned = Object.assign({}, obj);
console.log(
  spread.x,
  spread.y,
  spread.greet,
  assigned.y,
  Object.keys(spread).length
);

const wm = new WeakMap();
class Counter {
  #id;
  static #nextId = 0;
  constructor() {
    this.#id = Counter.#nextId++;
    wm.set(this, { count: 0, id: this.#id });
  }
  inc() {
    const data = wm.get(this);
    data.count++;
    return data.count;
  }
}
const a = new Counter();
const b = new Counter();
a.inc(); a.inc();
b.inc();
console.log(`${a.inc()} ${b.inc()} ${wm.has(a)} ${wm.get(a).id} ${wm.get(b).id}`);

const createCounterModule = (() => {
  let instances = 0;
  return function() {
    instances++;
    let count = 0;
    return {
      increment() { count++; return count; },
      id: instances
    };
  };
})();

const a = createCounterModule();
const b = createCounterModule();
console.log(a.increment(), a.increment(), b.increment(), a.id, b.id);

export {};