JavaScript test

function task1() {
  console.log('A');
  setTimeout(() => console.log('B'), 0);
  Promise.resolve().then(() => console.log('C'));
  Promise.resolve().then(() => setTimeout(() => console.log('D'), 0));
  Promise.resolve().then(() => console.log('E'));
  setTimeout(() => console.log('F'), 0);
  console.log('G');
}

task1();

async function foo() {
  console.log('Start');
  await Promise.resolve().then(() => {
    console.log('Inside Promise');
  });
  console.log('End');
}

foo();
console.log('Outside');

const person = {
  name: 'Alice',
  greet() {
    return `Hello, I'm ${this.name}`;
  },
  farewell: () => `Goodbye from ${this.name}`
};

const greetFn = person.greet;
const farewellFn = person.farewell;

console.log(person.greet());
console.log(greetFn());
console.log(farewellFn());

const x = [1, 2, 3];
const y = x;
y.push(4);
console.log(x);

const products = [
  { id: 1, name: 'Laptop', price: 1200, category: 'Electronics' },
  { id: 2, name: 'Headphones', price: 100, category: 'Electronics' },
  { id: 3, name: 'Book', price: 15, category: 'Books' },
  { id: 4, name: 'Shirt', price: 25, category: 'Clothing' },
  { id: 5, name: 'Coffee Mug', price: 10, category: 'Kitchen' }
];

const result = products
  .filter(p => p.price > 20)
  .map(p => ({ name: p.name, value: p.price * 0.9 }))
  .reduce((acc, item) => {
    acc.names.push(item.name);
    acc.total += item.value;
    return acc;
  }, { names: [], total: 0 });

console.log(result);

function recursiveReverseString(str) {
  return str === "" ? str : recursiveReverseString(str.substr(1)) + str[0];
}

const result = recursiveReverseString("hello");

console.log(result);

const handler = {
  get(target, prop, receiver) {
    if (prop === 'secret') {
      return Reflect.get(...arguments) + ' exposed';
    }
    return Reflect.get(...arguments);
  }
};

const secretObj = { secret: 'hidden', reveal: 'nothing' };
const proxy = new Proxy(secretObj, handler);

console.log(proxy.secret);

function createCounter() {
  let count = 0;
  return {
    increment: () => ++count,
    getCount: () => count
  };
}

function compose(...fns) {
  return (x) => fns.reduceRight((acc, fn) => fn(acc), x);
}

const counter = createCounter();
const double = x => x * 2;
const addOne = x => x + 1;

const incrementAndProcess = compose(double, addOne, counter.increment);

counter.increment();
const result = incrementAndProcess();
console.log(result);

const wMap = new WeakMap();

function foo() {
   wMap.set(this, 1);
};
const bar = () => wMap.set(this, 2);

bar();
foo();

console.log(wMap.get(this));

const user = {
  details: {
    name: 'Alex',
    contact: null,
    preferences: {
      theme: 'dark'
    }
  },
  getInfo() {
    return this?.details?.contact?.email || 
           this?.details?.preferences?.theme || 
           this?.details?.name || 
           'Unknown';
  }
};

console.log(user.getInfo());

var i = 5;

const arr = new Array(5);
arr.forEach(() => i++);

console.log(i);

async function foo() {
  console.log('Start');
  await Promise.resolve().then(() => {
    console.log('Inside Promise');
  });
  console.log('End');
}

foo();
console.log('Outside');

Promise.resolve(1)
.then(r => Promise.reject(r))
.catch(console.log)
.then(() => console.log(2));

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

const result = numbers
  .filter(num => num % 2 === 0)
  .map(num => num * 2)
  .reduce((acc, num, index, array) => {
    if (index === array.length - 1) {
      return (acc + num) / array.length;
    }
    return acc + num;
  }, 0);

console.log(result);

const person = {};
person.name.toUpperCase();
console.log(person.name);

class EventEmitter {
  constructor() {
    this.events = {};
  }
  
  on(event, listener) {
    if (!this.events[event]) {
      this.events[event] = [];
    }
    this.events[event].push(listener);
    return () => this.off(event, listener);
  }
  
  off(event, listener) {
    if (!this.events[event]) return;
    this.events[event] = this.events[event].filter(l => l !== listener);
  }
  
  emit(event, ...args) {
    if (!this.events[event]) return false;
    this.events[event].forEach(listener => listener(...args));
    return true;
  }
}

const emitter = new EventEmitter();
const unsubscribe = emitter.on('message', data => console.log(data));
emitter.emit('message', 'Hello');
emitter.emit('message', 'World');
unsubscribe();
emitter.emit('message', 'Ignored');
console.log(emitter.emit('message', 'Still ignored'));

const num = 10;
const add = () => {
   console.log(num + num);
};

(function () {
   const num = 5;
   add();
})();

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

const multiply = curry((a, b, c) => a * b * c);
const double = multiply(2);
const result = double(3)(4);

console.log(result);

function Foo() {
  this.bar = 1;
}

Foo.prototype.bar = 2;

const foo = new Foo();
console.log(foo.bar);