function trickyQuestion() {
    var a = 1;
    var b = 2;

    return (function() {
        delete a;
        delete b;
        return a + b;
    })();
}

console.log(trickyQuestion());

const arr = [1, 2, 3];
arr[-1] = 10;
console.log(arr.length, arr[-1], arr[2], arr[-2]);

let a = 5; // binary: 0101
let b = 3; // binary: 0011
let c = a & b; // binary: 0001
let d = a | b; // binary: 0111
let e = a ^ b; // binary: 0110

console.log(c, d, e);

const weakMap = new WeakMap();
const array = [1, 2, 3];
const obj = {};

weakMap.set(obj, array);

const result = weakMap.get(obj).map((acc, val) => acc + val);

console.log(result);

const original = Object.freeze({ a: [1, 2, 3] });
const copy = { ...original };

copy.a.push([...copy.a, ...original.a]);

console.log(original.a);
console.log(copy.a);

function trickyFunction(a) {
    a = a || 42;
    let result = (function(a) {
        return a * 2;
    })(a);
    return result;
}

console.log(trickyFunction(0));

const arr = [1, 2, 3, 4];
const newArr = arr.slice(0, 2);
console.log(newArr);

var arr=[1,2,3,4,5];
console.log(arr.reduce((a,b)=>a*b,"."));

let a = 'b';
let b = 'c';

(function () {
   console.log(a);
   a = 'd';
   b = 'e';
   console.log(b);
})();

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

const string = "JavaScript test";
const result = string.split(" ").map(word => word.length);
console.log(result);

let x = 1;
function outer() {
  let x = 2;
  function inner() {
    console.log(x);
    let x = 3;
  }
  inner();
}
outer();

const user = {
  name: 'John',
  greet() {
    const getName = () => {
      console.log(this.name);
    };
    getName();
  },
  farewell: function() {
    function getName() {
      console.log(this.name);
    }
    getName();
  }
};

user.greet();
user.farewell();

var i = 5;

const arr = new Array(5);
arr.forEach(() => i++);

console.log(i);

const obj = { value: 10 };
const result = (obj.value += 10);
console.log(result);

const arr = [1, 2, 3, 4, 5];
const result = arr
  .map(x => x * 2)
  .filter(x => x > 5)
  .reduce((acc, val) => {
    return acc + (val % 3 === 0 ? val : 0);
  }, 0);

console.log(result);

class MyClass {
  constructor() {
    this.a = 100;
  }
}
MyClass.prototype.b = 200;
const obj = new MyClass();
delete obj.b;
console.log(obj.a);

const items = new WeakSet();
const obj1 = { id: 1 };
const obj2 = { id: 2 };

items.add(obj1);
items.add(obj2);

obj2.value = 'test';
console.log(items.has(obj2));

obj2 = null;
setTimeout(() => {
  console.log(items.has(obj2));
}, 0);

Number.prototype[Symbol.iterator] = function*() { yield *['a','b','c','d'] };
console.log([...10]);

function* range(start, end) {
  let current = start;
  while (current <= end) {
    if (current % 3 === 0) {
      current++;
      continue;
    }
    yield current++;
  }
}

const gen = range(4, 10);
const result = [...gen];
console.log(result);