let obj = { name: 'Sarah', age: 25 };
let weakMap = new WeakMap();
let map = new Map();

weakMap.set(obj, 'weak reference');
map.set(obj, 'strong reference');

console.log(weakMap.has(obj));
console.log(map.has(obj));

obj = null;

console.log(weakMap.has(null));
console.log(map.has(null));
console.log(map.size);

const weakMap = new WeakMap();
const objs = [{}, {}, {}];

objs.forEach((obj, index) => weakMap.set(obj, index + 1));

const result = objs.filter(obj => weakMap.has(obj)).map(obj => weakMap.get(obj) * 2);

console.log(result);

const target = { name: 'Sarah', age: 25 };
const handler = {
  get(obj, prop) {
    if (prop === 'toString') {
      return () => `Person: ${obj.name}`;
    }
    return Reflect.get(obj, prop);
  },
  has(obj, prop) {
    return prop !== 'age' && Reflect.has(obj, prop);
  }
};
const proxy = new Proxy(target, handler);
console.log(proxy.name);
console.log('age' in proxy);
console.log(proxy.toString());

const obj = {};
obj.length = 5;
console.log(obj.length);

const array = [1, 2, 3, 4];
const result = array.reduceRight((acc, val) => acc - val);

console.log(result);

function createCounter() {
  let count = 0;
  
  return {
    increment() {
      return ++count;
    },
    reset() {
      const oldCount = count;
      count = 0;
      return oldCount;
    }
  };
}

const counterA = createCounter();
const counterB = createCounter();

counterA.increment();
counterA.increment();
counterB.increment();
const result = counterA.reset() + counterB.reset();
console.log(result);

const user = {
  profile: {
    settings: {
      theme: 'dark',
      notifications: null
    }
  }
};

const result1 = user?.profile?.settings?.theme;
const result2 = user?.profile?.settings?.notifications?.email;
const result3 = user?.profile?.preferences?.language ?? 'en';
const result4 = user?.profile?.settings?.notifications?.push?.('test');

console.log(result1, result2, result3, result4);

const original = {
  name: 'Sarah',
  hobbies: ['reading', 'coding'],
  address: { city: 'Portland', zip: 97201 }
};

const shallow = { ...original };
const deep = JSON.parse(JSON.stringify(original));

shallow.name = 'Emma';
shallow.hobbies.push('hiking');
shallow.address.city = 'Seattle';

deep.hobbies.push('swimming');
deep.address.zip = 98101;

console.log(original.hobbies.length, original.address.city);

var str="My name is John";
var words1=str.split(" ",3);
console.log("words1:",words1);
var words2=str.split(" ",5);
console.log("words2:",words2);

class SimpleObservable {
  constructor(subscribeFn) {
    this.subscribeFn = subscribeFn;
  }
  
  subscribe(observer) {
    return this.subscribeFn(observer);
  }
}

const obs = new SimpleObservable(observer => {
  observer.next('first');
  observer.next('second');
  observer.complete();
});

const results = [];
obs.subscribe({
  next: val => results.push(val),
  complete: () => results.push('done')
});

console.log(results.join('-'));

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

const result = numbers
  .map(n => n * 2)
  .filter(n => n > 5)
  .reduce((acc, n, index) => {
    acc.sum += n;
    acc.indices.push(index);
    return acc;
  }, { sum: 0, indices: [] });

console.log(result.sum);
console.log(result.indices);

const user = {
  name: 'Sarah',
  age: 25,
  getName() { return this.name; },
  getAge: () => this.age
};

const methods = {
  regular: user.getName,
  arrow: user.getAge
};

console.log(methods.regular());
console.log(methods.arrow());
console.log(user.getName());
console.log(user.getAge());

const data = '{"users": [{"name": "Sarah", "age": 25}, {"name": "Mike", "age": null}]}';

try {
  const parsed = JSON.parse(data);
  const result = parsed.users.map(user => {
    return user.age ?? 'unknown';
  });
  console.log(result.join(' - '));
} catch (error) {
  console.log('Parse error occurred');
}

const invalidJson = '{"name": "John", age: 30}';
try {
  JSON.parse(invalidJson);
  console.log('Success');
} catch {
  console.log('Invalid');
}

class Logger {
  log(msg) {
    return `[LOG]: ${msg}`;
  }
}

class Formatter {
  format(text) {
    return text.toUpperCase();
  }
}

class Service {
  constructor(logger, formatter) {
    this.logger = logger;
    this.formatter = formatter;
  }
  
  process(data) {
    const formatted = this.formatter.format(data);
    return this.logger.log(formatted);
  }
}

const service = new Service(new Logger(), new Formatter());
console.log(service.process('hello world'));

try {
  try {
    // Creating a custom error type
    class CustomError extends Error {
      constructor(message) {
        super(message);
        this.name = "CustomError";
      }
    }
    
    const fn = () => {
      throw new CustomError("Something went wrong");
    };
    
    try {
      fn();
    } catch (e) {
      throw new TypeError("Type error occurred");
    }
  } catch (e) {
    console.log(e instanceof Error, e.name, e instanceof TypeError);
  }
} catch (e) {
  console.log("Outer catch", e.message);
}