function makeCounters() {
  const counters = [];
  for (var i = 0; i < 3; i++) {
    let j = i;
    counters.push(() => `${i}-${j}`);
  }
  return counters;
}
const [a, b, c] = makeCounters();
console.log(a(), b(), c());
export {};

const a = Math.max();
const b = Math.min();
const c = 0.1 + 0.2 === 0.3;
const d = Math.max(1, NaN, 3);
const e = [1, 2, 3].reduce((sum, n) => sum + n, 0) / 3;
const f = Number.isInteger(5.0);
console.log(a, b, c, d, e, f);

const arr = [1, [2, 3], { a: 4 }];
const copy = [...arr];
copy[1].push(99);
copy[2].a = 100;
arr[0] = 999;

console.log(arr[0], arr[1], arr[2].a, copy[0]);

function makeFns() {
  const result = [];
  for (var i = 0; i < 3; i++) {
    let j = i;
    result.push(() => i + j);
  }
  return result;
}
const fns = makeFns();
console.log(fns.map(f => f()).join(','));

class Base {}
class Derived extends Base {
  static [Symbol.hasInstance](instance) {
    return false;
  }
}
const d = new Derived();
console.log(d instanceof Derived, d instanceof Base, Object.getPrototypeOf(Derived) === Base);

function* inner() {
  yield 1;
  yield 2;
  return 'inner-done';
}

function* outer() {
  const result = yield* inner();
  yield result;
  yield 3;
}

const gen = outer();
const results = [];
let r = gen.next();
while (!r.done) {
  results.push(r.value);
  r = gen.next();
}
console.log(results.join(','));

export {};

const compose = (...fns) => x => fns.reduceRight((acc, fn) => fn(acc), x);
const pipe = (...fns) => x => fns.reduce((acc, fn) => fn(acc), x);

const inc = x => x + 1;
const double = x => x * 2;
const square = x => x * x;

const f = compose(square, double, inc);
const g = pipe(square, double, inc);

console.log(f(2), g(2));

const compose = (...fns) => x => fns.reduceRight((acc, fn) => fn(acc), x);
const pipe = (...fns) => x => fns.reduce((acc, fn) => fn(acc), x);

const add = n => x => x + n;
const mul = n => x => x * n;

const composed = compose(add(3), mul(2));
const piped = pipe(add(3), mul(2));

console.log(composed(5), piped(5));

const proto = { inherited: 'nope' };
const obj = Object.create(proto);
obj.b = 2;
obj[1] = 'one';
obj.a = 1;
Object.defineProperty(obj, 'hidden', { value: 'secret', enumerable: false });
obj[Symbol('sym')] = 'symbolValue';
console.log(
  Object.keys(obj).join(','),
  Object.values(obj).join(','),
  Object.entries(obj).length
);