How to put an array into another array without concatenating all elements?

Question

JavaScript

var firstArray = ['cat', 'dog', 'elephant'];
var secondArray = ['blue', 'orange', 'grey'];
The end result should look like this:
var newArray = ['cat', 'dog', 'elephant', ['blue', 'orange', 'grey']];

Answer 1

let newArray = [...firstArray, secondArray];