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

const counter = createCounter();

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

const obj = { a: 1, b: 2, c: 3 };
const result = Object.values(obj).reduce((acc, curr) => acc * curr, 1);
console.log(result);

console.log(1);

setTimeout(() => {
  console.log(2);
}, 100);

setTimeout(() => {
  console.log(3);
}, 0);

Promise.resolve().then(() => {
  console.log(4);
}).then(() => {
  console.log(5);
});

console.log(6);

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

const result = data.reduce((acc, val) => acc.concat(Array.from({ length: val }, (_, index) => val + index)), []);

console.log(result);

function createSymbolDemo() {
  const obj = {};
  
  const sym1 = Symbol('description');
  const sym2 = Symbol('description');
  const sym3 = Symbol.for('shared');
  const sym4 = Symbol.for('shared');
  
  obj[sym1] = 'Value 1';
  obj[sym2] = 'Value 2';
  obj[sym3] = 'Value 3';
  obj[sym4] = 'Value 4';
  
  console.log(Object.keys(obj).length, sym1 === sym2, sym3 === sym4, obj[sym3]);
}

createSymbolDemo();

const obj = {
  [Symbol('a')]: 'hidden',
  [Symbol.for('b')]: 'registered',
  c: 'normal'
};

const symbols = Object.getOwnPropertySymbols(obj);
const keys = Object.keys(obj);
const allProps = Reflect.ownKeys(obj);

console.log(symbols.length, keys.length, allProps.length);

const user = {
  name: 'Sarah',
  age: 25,
  greet() {
    return `Hello, I'm ${this.name}`;
  }
};

const keys = Object.keys(user);
const values = Object.values(user);
const entries = Object.entries(user);

console.log(keys.length);
console.log(values.includes('Sarah'));
console.log(entries[2][0]);

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

const result = data.reduce((acc, val) => acc.concat(Array.from({ length: val }, (_, index) => val + index)), []);

console.log(result);

const user = {
  name: 'Sarah',
  profile: {
    settings: {
      theme: 'dark'
    }
  }
};

const config = {
  name: 'John',
  profile: null
};

console.log(user.profile?.settings?.theme);
console.log(config.profile?.settings?.theme);
console.log(user.profile?.preferences?.language);
console.log(config.profile?.settings?.theme ?? 'light');

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);

const target = { name: 'Sarah', age: 25 };
const handler = {
  get(obj, prop) {
    if (prop in obj) {
      return obj[prop].toString().toUpperCase();
    }
    return `Property ${prop} not found`;
  },
  set(obj, prop, value) {
    obj[prop] = value * 2;
    return true;
  }
};
const proxy = new Proxy(target, handler);
proxy.salary = 50000;
console.log(proxy.name);
console.log(proxy.age);
console.log(proxy.salary);
console.log(proxy.city);

function testScope() {
  var x = 'outer';
  let y = 'outer';
  
  if (true) {
    var x = 'inner';
    let y = 'inner';
    console.log(x, y);
  }
  
  console.log(x, y);
}

testScope();

class Rectangle {
  constructor(width, height) {
    this.width = width;
    this.height = height;
  }

  get area() {
    return this.width * this.height;
  }
}

const rectangle = new Rectangle(5, 10);
console.log(rectangle.area());

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();

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 * x;
const negate = (x) => -x;

const transform1 = compose(negate, square, addTen, double);
const transform2 = pipe(double, addTen, square, negate);

const input = 3;

console.log(transform1(input));
console.log(transform2(input));
console.log(transform1(input) === transform2(input));

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

let columnSums = [];

for (let i = 0; i < matrix[0].length; i++) {
  let sum = 0;
  for (let j = 0; j < matrix.length; j++) {
    sum += matrix[i][i];
  }
  columnSums.push(sum);
}
console.log(columnSums);

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

const activeSessions = new WeakSet();

const s1 = new Session("user_42");
const s2 = new Session("user_99");
let s3 = new Session("user_07");

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

console.log(activeSessions.has(s1));         // line A
console.log(activeSessions.has(s3));         // line B

s3 = null;

console.log(activeSessions.has(s3));         // line C

activeSessions.delete(s2);
console.log(activeSessions.has(s2));         // line D
console.log(activeSessions.size);            // line E

var a = 5;
function test() {
  console.log(a);
  var a = 10;
  console.log(a);
}

test();

const inventory = {
  apples: 5,
  bananas: 0,
  cherries: 12,
  dates: undefined,
  elderberries: null,
};

const summary = Object.entries(inventory)
  .filter(([_, value]) => value)
  .reduce((acc, [key, value]) => {
    acc[key] = value * 2;
    return acc;
  }, {});

console.log(Object.keys(summary).length);
console.log(Object.values(summary).every(v => v > 10));
console.log(Object.keys(inventory).length === Object.keys(summary).length);

const user = {
  profile: {
    name: "Alice",
    settings: null
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

const admin = {
  profile: {
    name: "Admin"
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

console.log(user.getPreferences());
console.log(admin.getPreferences());
console.log(user.profile.extra?.id?.toString());

var a=[1,2,3,4,5];
console.log(a.some(x=>x>4)); 
console.log(a.some(x=>x>5));