var cars = ["camry", "corolla", "toyota", "honda", "ford", "bmw", "audi", "mercedes", "volkswagen", "tesla", "lamborghini"];

var x = 30;

var gen = setInterval(function generate() {
  var text = document.getElementById("child-box");
  var random = Math.floor(Math.random() * cars.length);
  text.innerHTML = cars[random];
  var time = document.getElementById("timing").innerText = --x;

  if (x == 0) {
    clearInterval(gen);
  }
}, 1000);

function gen() {
  generate();
  document.getElementById("clicked").addEventListener('click', generate);
}