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

let arr = [1, 2, 3, 4];
arr.pop();

function sum(a, b = 2) {
  return a + b;
}
console.log(sum(3));

let obj = { name: "John" };
let obj2 = obj;
obj2.name = "Doe";
console.log(obj.name);

const numbers = [1, 2, 3, 4];
const squared = numbers.map(num => num * num);
console.log(squared);

let x = 10;
function foo() {
  console.log(x);
  let x = 20;
}
foo();

let arr = [1, 2, 3];
arr.length = 0;
console.log(arr);

let a = {};
let b = { key: "b" };
let c = { key: "c" };

a[b] = 123;
a[c] = 456;

console.log(a[b]);