const wm = new WeakMap();
const obj1 = {};
const obj2 = {};
const obj3 = obj1;

wm.set(obj1, 'first');
wm.set(obj2, 'second');
wm.set(obj3, 'third');

console.log(wm.get(obj1));
console.log(wm.get(obj2));
console.log(wm.get(obj3));
console.log(wm.has(obj1));
console.log(wm.size);

const data = '{"name": "Maria", "age": 25, "skills": ["JavaScript", "Python"]}';

try {
  const parsed = JSON.parse(data);
  const modified = {
    ...parsed,
    age: parsed.age + 5,
    skills: [...parsed.skills, "TypeScript"]
  };
  
  const serialized = JSON.stringify(modified, null, 0);
  const reparsed = JSON.parse(serialized);
  
  console.log(reparsed.skills.length);
  console.log(typeof reparsed.age);
} catch (error) {
  console.log('Parse error');
}

const numbers = [1, 2, 3, 4, 5];

const pipeline = (...fns) => (value) => fns.reduce((acc, fn) => fn(acc), value);

const multiply = (x) => (y) => x * y;
const add = (x) => (y) => x + y;
const square = (x) => x * x;

const transform = pipeline(
  multiply(2),
  add(3),
  square
);

const result = numbers.map(transform);
console.log(result);

function Vehicle(type) {
  this.type = type;
}

Vehicle.prototype.describe = function() {
  return `This is a ${this.type}`;
};

function Car(brand) {
  Vehicle.call(this, 'car');
  this.brand = brand;
}

Car.prototype = Object.create(Vehicle.prototype);
Car.prototype.constructor = Car;

Car.prototype.describe = function() {
  return Vehicle.prototype.describe.call(this) + ` made by ${this.brand}`;
};

const tesla = new Car('Tesla');
console.log(tesla.describe());
console.log(tesla.constructor.name);

const Maybe = {
  of: (value) => ({ value, map: f => value == null ? Maybe.nothing() : Maybe.of(f(value)) }),
  nothing: () => ({ value: null, map: () => Maybe.nothing() })
};

const result = Maybe.of(5)
  .map(x => x * 2)
  .map(x => x > 15 ? null : x)
  .map(x => x + 1)
  .map(x => x.toString());

console.log(result.value);

class EventManager {
  constructor() {
    this.listeners = new Map();
  }
  
  addListener(event, callback) {
    if (!this.listeners.has(event)) {
      this.listeners.set(event, new Set());
    }
    this.listeners.get(event).add(callback);
  }
  
  removeAllListeners() {
    this.listeners.clear();
  }
}

const manager = new EventManager();
const obj = { data: new Array(1000).fill('memory') };
manager.addListener('test', () => obj.data.length);
manager.removeAllListeners();
console.log(manager.listeners.size);