const updateScrollPercentage = function () {
const heightOfWindow = window.innerHeight,
contentScrolled = window.pageYOffset,
bodyHeight = document.body.offsetHeight,
percentage = document.querySelector("[data-scrollPercentage] .percentage")
percentageVal = document.querySelector("#percentage-value")

if (bodyHeight - contentScrolled <= heightOfWindow) {
percentageVal.textContent = percentage.style.width = "100%"
}
else {
const total = bodyHeight - heightOfWindow,
got = contentScrolled,
percent = parseInt((got / total) * 100)
percentageVal.textContent = percentage.style.width = percent + "%"
}
}

window.addEventListener('scroll', updateScrollPercentage)