javascript array concat spread operator

const arr1 = [1,2,3]
const arr2 = [4,5,6]
const arr3 = [...arr1, ...arr2] //arr3 ==> [1,2,3,4,5,6]

const a = ['to', 'code'];
const b = ['learning', ...a, 'is', 'fun']; 
console.log(b); //> ['learning', 'to', 'code', 'is', 'fun']

var hege = ["Cecilie", "Lone"];

var stale = ["Emil", "Tobias", "Linus"];

var kai = ["Robin"];

var children = hege.concat(stale, kai);