const handler = {
  get(target, prop, receiver) {
    if (prop in target) {
      return Reflect.get(target, prop, receiver) * 2;
    }
    return `missing:${prop}`;
  },
  set(target, prop, value) {
    if (typeof value !== "number") {
      throw new TypeError("Only numbers allowed");
    }
    Reflect.set(target, prop, value + 10);
    return true;
  },
  has(target, prop) {
    return prop.startsWith("x") ? false : prop in target;
  },
};

const store = new Proxy({ xray: 5, zoom: 8 }, handler);

store.nova = 3;
console.log(store.xray);
console.log(store.nova);
console.log(store.ghost);
console.log("zoom" in store);
console.log("xray" in store);

const compose = (...fns) => x => fns.reduceRight((acc, fn) => fn(acc), x);
const pipe = (...fns) => x => fns.reduce((acc, fn) => fn(acc), x);

const double = x => x * 2;
const addTen = x => x + 10;
const square = x => x ** 2;
const negate = x => -x;

const composed = compose(negate, square, addTen, double);
const piped = pipe(negate, square, addTen, double);

const val = 3;

console.log(composed(val)); // compose: right-to-left
console.log(piped(val));    // pipe: left-to-right

class Session {
  #id;
  constructor(id) {
    this.#id = id;
  }
  getId() {
    return this.#id;
  }
}

const activeSessions = new WeakSet();

const s1 = new Session("alpha");
const s2 = new Session("beta");
let s3 = new Session("gamma");

activeSessions.add(s1);
activeSessions.add(s2);
activeSessions.add(s3);

console.log(activeSessions.has(s1));
console.log(activeSessions.has(s3));

activeSessions.delete(s2);
console.log(activeSessions.has(s2));

try {
  activeSessions.add("invalid");
} catch (e) {
  console.log(e instanceof TypeError);
}

console.log(activeSessions.has(s1));

const handler = {
  get(target, prop, receiver) {
    if (prop in target) {
      return Reflect.get(target, prop, receiver) * 2;
    }
    return Reflect.get(target, prop, receiver);
  },
  set(target, prop, value, receiver) {
    if (typeof value !== "number") return false;
    return Reflect.set(target, prop, value * 3, receiver);
  },
  has(target, prop) {
    return prop.startsWith("x") && Reflect.has(target, prop);
  },
};

const obj = new Proxy({ x1: 10, y1: 20 }, handler);
obj.x2 = 15;
obj.y2 = 40;

console.log(obj.x1);
console.log(obj.x2);
console.log("x1" in obj);
console.log("y1" in obj);
console.log(obj.y2);

function* range(start, end) {
  while (start < end) {
    yield start++;
  }
}

function* labeled(prefix, gen) {
  for (const val of gen) {
    yield `${prefix}:${val}`;
  }
}

function* pipeline() {
  yield* labeled("A", range(1, 4));
  yield* labeled("B", range(10, 12));
}

const results = [...pipeline()];
console.log(results.length, results[0], results[results.length - 1]);

function Vehicle(make, model, year) {
  this.make = make;
  this.model = model;
  this.year = year;
  this.describe = function () {
    return `${this.year} ${this.make} ${this.model}`;
  };
}

Vehicle.prototype.age = function (currentYear) {
  return currentYear - this.year;
};

const car = new Vehicle("Toyota", "Supra", 1998);
const truck = new Vehicle("Ford", "Raptor", 2021);

console.log(car.describe());
console.log(truck.age(2025));
console.log(car.constructor === Vehicle);
console.log(Object.getPrototypeOf(car) === Vehicle.prototype);

function makeCounter(start = 0, step = 1) {
  let count = start;
  const history = [];

  return {
    increment() {
      count += step;
      history.push(count);
      return this;
    },
    decrement() {
      count -= step;
      history.push(count);
      return this;
    },
    getHistory: () => history,
    getCount: () => count,
  };
}

const counter = makeCounter(10, 3);
counter.increment().increment().decrement();

console.log(counter.getCount());
console.log(counter.getHistory());

var a = 0, b = 0, arr = [3, 6, 9, 6, 9, 3];
var data = arr.some((x, i)=>{
  a = arr[i]; 
  b = arr[i + 1];
  return a + b == 15
})
console.log(data)
console.log(a, b)

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);

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);

console.log(1);
setTimeout(() => console.log(2), 0);
Promise.resolve()
  .then(() => {
    console.log(3);
    return Promise.resolve(4);
  })
  .then(console.log);
console.log(5);

async function asyncFunc() {
  console.log('Async Start');
  await new Promise(resolve => setTimeout(resolve, 100));
  console.log('Async End');
}

console.log('Script Start');
asyncFunc();
setTimeout(() => console.log('Timeout 1'), 50);
setTimeout(() => console.log('Timeout 2'), 150);
console.log('Script End');

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('-'));

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

const counter = createCounter();
counter.increment();
counter.increment();
counter.decrement();

const { increment, reset } = counter;
increment();
reset();
increment();

console.log(counter.increment());

function Person(name) {
  this.name = name;
  this.sayName = () => console.log(this.name);
}

const person1 = new Person('David');
const person2 = { name: 'Not David', sayName: person1.sayName };

person2.sayName();

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');
}

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');
}