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')}`);

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) return fn.apply(this, args);
    return (...more) => curried.apply(this, [...args, ...more]);
  };
}

function multiply(a, b, c = 1, ...rest) {
  return a * b * c * (rest.reduce((s, n) => s + n, 0) || 1);
}

const curried = curry(multiply);
console.log(curried(2)(3), multiply.length);

const target = { a: 1, b: 2 };
const handler = {
  get(obj, prop, receiver) {
    if (prop in obj) {
      return Reflect.get(obj, prop, receiver);
    }
    return `missing:${String(prop)}`;
  },
  set(obj, prop, value, receiver) {
    if (typeof value === 'number') {
      return Reflect.set(obj, prop, value * 2, receiver);
    }
    return Reflect.set(obj, prop, value, receiver);
  }
};
const p = new Proxy(target, handler);
p.c = 5;
p.d = 'hello';
console.log(p.a, p.c, p.d, p.z);

const sym = Symbol('id');
const target = { a: 1, [sym]: 2 };
Reflect.defineProperty(target, 'b', { value: 3, enumerable: false });

const handler = {
  get(obj, prop, receiver) {
    if (prop === 'a') return Reflect.get(obj, prop, receiver) * 10;
    return Reflect.get(obj, prop, receiver);
  }
};

const proxy = new Proxy(target, handler);
console.log(proxy.a, proxy.b, Reflect.ownKeys(target).length, Object.keys(target).length);

let a = 0;
let b = null;
let c = '';
let d;

a ||= 10;
b ??= 20;
c &&= 'changed';
d ??= a + b;

console.log(a, b, c, d);

function build(a, b = a + 1, c = (() => a + b)()) {
  a = 100;
  return [a, b, c];
}
console.log(build(1), build(1, 2), build(5, 5, 5));

let outerType;
{
  function greet() {
    return 'inner';
  }
  outerType = typeof greet;
}
console.log(outerType, typeof greet);

const x = 2n ** 10n;
const y = 7n / 2n;
const z = -7n / 2n;
const w = BigInt(3.0) === 3n;
console.log(`${x} ${y} ${z} ${typeof x} ${w}`);

const obj = { a: { b: null, getC: () => 42 } };
let calls = 0;
function sideEffect() {
  calls++;
  return 10;
}
const result = obj.a?.b?.getC?.() ?? sideEffect();
const result2 = obj.a?.z?.getC?.() ?? sideEffect();
console.log(result, result2, calls);

const counter = {
  count: 0,
  *[Symbol.iterator]() {
    yield this.count++;
    yield this.count++;
    yield this.count++;
  }
};

console.log([...counter], counter.count);

export {};