script.js

var cube = document.querySelector(".cube");
var rollBtn = document.querySelector(".rollBtn");
var currentClass = "";

function getRandomInt(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min) + min);
  //The maximum is exclusive and the minimum is inclusive
}

function rollDice() {
  var randNum = getRandomInt(1, 7);
  console.log(randNum);
  var showClass = "show-" + randNum;
  console.log(showClass);
  if (currentClass) {
    cube.classList.remove(currentClass);
  }
  cube.classList.add(showClass);
  currentClass = showClass;
}
// set initial side
rollDice();

rollBtn.addEventListener("click", rollDice);