const nums = [1, 2, 3, 4, 5];
const result = nums
  .filter(n => n % 2 !== 0)
  .map(n => n ** 2)
  .reduce((acc, n) => acc + n, 0);

const arr = [10, , 20, undefined, 30];
const mapped = arr.map(x => x * 2);

console.log(result, mapped);

let i = 0;
const key = () => `k${i++}`;
const obj = {
  [key()]: i,
  [key()]: i,
  [key()]: i,
};
console.log(Object.keys(obj).join(','), obj.k0, obj.k1, obj.k2);

const a = 5 & 3;
const b = 5 | 2;
const c = ~5;
const d = 1 << 31;
const e = -1 >>> 28;
const f = 5 ^ 5;
console.log(a, b, c, d, e, f);

'use strict';

function getValue() {
  return this.value;
}

const obj = { value: 42, getValue };
const fn = obj.getValue;

try {
  fn();
} catch (err) {
  console.log(err.constructor.name, typeof this);
}

console.log(
  typeof typeof 1,
  1 + typeof 1,
  2 ** 3 ** 2,
  1 + 2 + '3',
  1 < 2 < 3,
  3 > 2 > 1
);

function Foo(x) {
  this.x = x;
  return { x: x * 2 };
}

function Bar(x) {
  this.x = x;
  return 42;
}

const f = new Foo(5);
const b = new Bar(5);

console.log(f.x, b.x, f instanceof Foo, b instanceof Bar);

function* inner() {
  yield 1;
  yield 2;
  return 100;
}

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

const it = outer();
console.log(it.next().value, it.next().value, it.next().value, it.next().value);

class Base {
  static count = 0;
  static increment() {
    this.count++;
    return this.count;
  }
}

class Derived extends Base {
  static count = 10;
}

console.log(Base.increment(), Derived.increment(), Base.count, Derived.count);

let counter = 0;
const mod = {
  get counter() { return counter; },
  increment() { counter++; }
};

const { counter: snapshotCounter } = mod;
mod.increment();
mod.increment();

console.log(snapshotCounter, mod.counter, counter);

const obj = {
  value: 42,
  getValue() { return this?.value; },
  getValueArrow: () => this?.value
};
const { getValue, getValueArrow } = obj;
console.log(obj.getValue(), getValue(), obj.getValueArrow(), getValueArrow());