let obj = { a: 1 };
Object.freeze(obj);

console.log(Object.isFrozen(obj));
console.log(obj.a = 2);
console.log(obj.a);

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());

let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };
let obj3 = { ref: obj1 };

obj1.circular = obj1;
obj2.partner = obj3;
obj3.partner = obj2;

let weakMap = new WeakMap();
weakMap.set(obj1, 'data1');
weakMap.set(obj2, 'data2');

obj1 = null;
obj2 = null;

console.log(weakMap.has(obj3.ref));
console.log(obj3.partner.name);

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

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

const counter1 = createCounter();
const counter2 = createCounter();
counter1.increment();
counter1.increment();
counter2.increment();
console.log(counter1.get(), counter2.get());
const { increment, get } = counter1;
increment();
console.log(get());

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

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

console.log('Hi' instanceof String);

const promise1 = Promise.resolve('first');
const promise2 = new Promise(resolve => {
  resolve('second');
});

const promise3 = Promise.resolve().then(() => 'third');

async function test() {
  console.log('start');
  
  const result1 = await promise1;
  console.log(result1);
  
  const result2 = await promise2;
  console.log(result2);
  
  const result3 = await promise3;
  console.log(result3);
  
  console.log('end');
}

test();

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

const matrix = [
  [2, 4],
  [6, 8],
];

const result = matrix.reduceRight((acc, row) => acc.concat(row.map(num => num * 2)), []);

console.log(result);

const firstArrayData = [ 'JavaScript', 'Universe' ];
const secondArrayData = [ 'JavaScript', 'Universe' ];

console.log(firstArrayData == secondArrayData);
console.log(firstArrayData === secondArrayData);

const sym1 = Symbol("id");
const sym2 = Symbol("id");
console.log(sym1 === sym2);

const original = { a: 1, b: { c: 2 } };
const shallow = { ...original };
const deep = JSON.parse(JSON.stringify(original));

shallow.a = 10;
shallow.b.c = 20;

deep.a = 100;
deep.b.c = 200;

const frozen = Object.freeze({ x: 1, y: { z: 2 } });
frozen.x = 99;
frozen.y.z = 99;

console.log(original.a, original.b.c, frozen.x, frozen.y.z);

let funcs = [];

for (var i = 0; i < 3; i++) {
  funcs.push(() => i);
}

console.log(funcs[0]());
console.log(funcs[1]());
console.log(funcs[2]());

async function fetchData() {
  console.log('1');
  return Promise.resolve('data');
}

async function processData() {
  console.log('2');
  const result = await fetchData();
  console.log('3');
  return result;
}

console.log('4');
processData().then(() => console.log('5'));
console.log('6');

const person = {
  name: "John",
  greet: function() {
    const getMessage = () => `Hello, ${this.name}`;
    return getMessage();
  }
};

console.log(person.greet());

const arr = new Array(1000000).fill(0).map((_, i) => i);
const results = [];

function method1() {
  return arr.filter(x => x % 2 === 0).map(x => x * 2).slice(0, 3);
}

function method2() {
  const result = [];
  for (let i = 0; i < arr.length && result.length < 3; i++) {
    if (arr[i] % 2 === 0) {
      result.push(arr[i] * 2);
    }
  }
  return result;
}

console.log(method1().join(','));
console.log(method2().join(','));

function* infiniteGenerator() {
  let i = 0;
  while (true) {
    yield i++;
  }
}

const weakMap = new WeakMap();
const gen = infiniteGenerator();

weakMap.set(gen, gen.next().value);

const result = weakMap.get(gen) + gen.next().value;

console.log(result);

const words = ['a', 'b', 'c'];
const result = words.concat(1, 2, 3);
console.log(result);

function foo() {
   return typeof arguments;
};
console.log(foo(1, 2, 3));

const a = { value: 1 };
const b = Object.create(a);
b.value = 2;

console.log(b.value);
console.log(a.value);