let percent = document.getElementById("percent");
let advances;

let percentage = 0;
let interval;

function updatePercent(increment=NaN) {
  advances = true;
  if (isNaN(increment)) {
    increment = Math.floor(Math.random() * 20);
  }
  if (percentage >= 80 && percentage < 99) {
    percentage = 99;
  } else {
    percentage += increment;
  }
  percent.textContent = percentage.toString() + "% complete";
  if (percentage == 99) {
    clearInterval(interval);
    setTimeout(() => {
      updatePercent(Math.floor(Math.random() * 12 + 2));
      interval = setInterval(updatePercent, 3000);
    }, 15000)
  }
}

interval = setInterval(updatePercent, 3000);