const map = new Map([
  ['a', 1],
  ['b', 2],
  ['c', 3]
]);

const key = { id: 'key' };
map.set(key, 4);
map.set(key, 5);

const result = [];
result.push(map.get('a'));
result.push(map.get(key));
result.push(map.size);
result.push(map.has({ id: 'key' }));

console.log(result);

const promise1 = Promise.resolve(10);
const promise2 = promise1.then(x => x * 2);
const promise3 = promise2.then(x => {
  console.log(x);
  return x + 5;
});
const promise4 = promise2.then(x => {
  console.log(x);
  return x * 3;
});
Promise.all([promise3, promise4]).then(results => {
  console.log(results);
});

const x = 5;
const y = 10;

const obj = {
  x,
  y,
  z: x + y,
  calculate() {
    return this.x * this.y;
  },
  [x + y]: 'computed'
};

console.log(obj.calculate() + obj[15] + obj.z);

const curry = (fn) => {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    }
    return (...nextArgs) => curried(...args, ...nextArgs);
  };
};

const multiply = (a, b, c) => a * b * c;
const curriedMultiply = curry(multiply);

const step1 = curriedMultiply(2);
const step2 = step1(3);
const result = step2(4);

console.log(result);

const a = { x: 1 };
const b = a;
const c = { x: 1 };

b.x = 2;
const d = b;
d.x = 3;

console.log(a.x);
console.log(b.x);
console.log(c.x);
console.log(a === b);
console.log(a === c);

class Subject {
  constructor() {
    this.observers = [];
  }
  attach(observer) {
    this.observers.push(observer);
  }
  notify(data) {
    this.observers.forEach(obs => obs.update(data));
  }
}

const subject = new Subject();
subject.attach({ update: (d) => console.log(d * 2) });
subject.attach({ update: (d) => console.log(d + 5) });
subject.notify(10);

const obj = { a: 1, b: 2, c: 3 };
Object.defineProperty(obj, 'd', { 
  value: 4, 
  enumerable: false 
});

const entries = Object.entries(obj);
const keys = Object.keys(obj);
const values = Object.values(obj);

console.log(entries.length + keys.length + values.length);