const regex = /^cat/gm;
const str = `dog
cat
bat`;
console.log(str.match(regex));

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

const regex = /\D+/;
const str = '123abc456';
console.log(str.match(regex)[0]);

const x = (() => {
  try {
    return 10;
  } finally {
    return 20;
  }
})();
console.log(x);

const regex = /\bcat\b/;
console.log(regex.test('concatenate'), regex.test('cat'), regex.test('scatter'));

let javascript_tests = 1000 

try { 
  javascript_tests = 550 
} finally { 
  javascript_tests = 64 
} 

console.log(javascript_tests)

const obj = {};
Object.defineProperty(obj, "prop", {
  value: 42,
  writable: false
});
obj.prop = 100;
console.log(obj.prop);

const arr = [...new Set([3, 1, 2, 3, 4])]
console.log(arr.length, arr[2])

const regex = /\d{2,}/;
console.log(regex.test('5'), regex.test('55'), regex.test('555'));

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

function processData({ a = 10, b = 20 } = { a: 30 }) {
  console.log(a, b);
}

processData({ a: 5 });
processData();

const regex = /(?<day>\d{2})-(?<month>\d{2})-(?<year>\d{4})/;
const str = '25-12-2020';
const { groups: { day, month, year } } = str.match(regex);
console.log(day, month, year);

const regex = /colou?r/;
console.log(regex.test('color'), regex.test('colour'), regex.test('colr'));

const regex = /^(?!cat).+$/;
console.log(regex.test('cat'), regex.test('dog'), regex.test('category'));

const obj = { a: 1 };
Object.seal(obj);
obj.b = 2;
console.log(obj.b);

const regex = /a/i;
console.log(regex.test('A'), regex.test('a'), regex.test('b'));

const regex = /(\w+)\s(\w+)/;
const str = 'Hello World';
const result = str.replace(regex, '$2', '$1');
console.log(regex);

console.log(0.1 + 0.2 === 0.3);

const obj = {
  a: 1,
  b: function() {
    return this.a;
  }
};
const b = obj.b;
console.log(b());

const string = "Hello, World! How are you?";

const result = [...string.matchAll(/[aeiou]/g)]
                 .map(match => match[0])
                 .reverse()
                 .join("");

console.log(result);