const user = {
  name: 'Alice',
  age: 30
};

const handler = {
  get(target, prop) {
    if (prop in target) {
      return target[prop];
    }
    return `Property '${prop}' doesn't exist`;
  },
  set(target, prop, value) {
    if (prop === 'age' && typeof value !== 'number') {
      console.log(`Error: ${value} is not a valid age`);
      return false;
    }
    target[prop] = value;
    return true;
  }
};

const userProxy = new Proxy(user, handler);
userProxy.age = '31';
userProxy.job = 'Developer';

console.log(userProxy.job);

function process(data) {
  try {
    if (!data) {
      throw new TypeError('No data provided');
    }
    
    if (Array.isArray(data)) {
      return data.map(item => item * 2);
    }
    
    if (typeof data === 'object') {
      return Object.keys(data);
    }
    
    return data.toString();
  } catch (error) {
    if (error instanceof TypeError) {
      return 'Type error occurred';
    }
    return 'Unknown error';
  }
}

console.log(process(null));

function Animal(name) {
  this.name = name;
}

Animal.prototype.speak = function() {
  return `${this.name} makes a noise.`;
};

function Dog(name) {
  Animal.call(this, name);
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.speak = function() {
  return `${this.name} barks.`;
};

const animal = new Animal('Rover');
const dog = new Dog('Rex');

console.log(dog instanceof Animal, dog.speak(), animal.speak(), Dog.prototype.isPrototypeOf(dog));

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<span>${values[i]}</span>` : '';
    return result + str + value;
  }, '');
}

const language = 'JavaScript';
const years = 10;

const result = highlight`I have been coding in ${language} for ${years} years`;
console.log(result);

function createCounter() {
  let count = 0;
  
  return {
    increment() {
      count++;
      return count;
    },
    decrement() {
      count--;
      return count;
    },
    getValue() {
      return count;
    }
  };
}

const counter1 = createCounter();
const counter2 = createCounter();

counter1.increment();
counter1.increment();
counter2.increment();
counter1.decrement();

console.log(counter1.getValue() + counter2.getValue());

class ShoppingCart {
  constructor() {
    if (ShoppingCart.instance) {
      return ShoppingCart.instance;
    }
    
    this.items = [];
    ShoppingCart.instance = this;
  }
  
  addItem(item) {
    this.items.push(item);
  }
  
  getItems() {
    return [...this.items];
  }
}

const cart1 = new ShoppingCart();
const cart2 = new ShoppingCart();

cart1.addItem('Book');
cart2.addItem('Laptop');

console.log(cart1.getItems());

const templateFn = (strings, ...values) => {
  return strings.reduce((result, str, i) => {
    const value = values[i] !== undefined ? 
      (typeof values[i] === 'number' ? values[i] * 2 : values[i]) : '';
    return result + str + value;
  }, '');
};

const num = 5;
const str = 'world';

const result = templateFn`Hello ${str}, ${num} times ${'!'}`;
console.log(result);