function combine(...arrays) {
  return arrays.reduce((acc, arr) => [...acc, ...arr], []);
}

const result = combine([1, 2], [3, 4], [5, 6]);
console.log(result);

const obj = {
  valueOf() {
    return 42;
  }
};

const result = obj + 8;
console.log(result);

function trickyFunction() {
    var a = 10;
    var b = a;
    b = 15;

    const obj1 = { x: 1 };
    const obj2 = obj1;
    obj2.x = 5;

    console.log(a + ' ' + b + ' ' + obj1.x);
}

trickyFunction();

function trickyFunction() {
  var x = 10;
  if (x > 5) {
    let y = x * 2;
    x = y;
  }
  return x;
}

console.log(trickyFunction());

function trickyFunction() {
  var obj = { a: 1 };
  var anotherObj = obj;
  obj.a = 2;
  obj = { a: 3 };
  anotherObj.a = 4;
  return obj.a + anotherObj.a;
}

console.log(trickyFunction());

async function fetchData() {
  let data = 'initial';

  const promise = new Promise((resolve) => {
    setTimeout(() => {
      resolve('fetched');
    }, 1000);
  });

  promise.then((result) => {
    data = result;
  });

  return data;
}

fetchData().then(console.log);

const WM = new WeakMap();
let obj = {};
let anotherObj = {};
WM.set(obj, 'object data');
WM.set(anotherObj, 'another object data');
obj = null;

// Let's check what's logged
console.log(WM.has(obj));
console.log(WM.has(anotherObj));