const avengers = ['Thor', 'The Hulk', 'Captain America'];
let guardians = ['Star Lord', 'Gamorra', 'Drax', 'Rocket', 'Groot'];
// Spread out arrays in a new array and put a new value in between them
const heroes = [...avengers, 'Loki', ...guardians];

// Adding new stuff to an array just got easier too
guardians = [...guardians, 'Mantis', 'Yondu', 'Nebula'];

// Or simply making a copy of an array
const avengersCopy = [...avengers];