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 {};

const base = {
  greet() { return `Hello, ${this.name}`; }
};
const mid = Object.create(base);
mid.name = 'Mid';
const child = Object.create(mid);
child.name = 'Child';

console.log(
  child.greet(),
  mid.greet(),
  Object.getPrototypeOf(child) === mid,
  child.hasOwnProperty('greet')
);

class StringBuilder {
  #parts = [];
  append(s) {
    this.#parts.push(s);
    return this;
  }
  toString() {
    return this.#parts.join('');
  }
}

const sb = new StringBuilder().append('a').append('b').append('c');
console.log(`${sb}-${sb.append('d')}`);