A little progress bar for scrolling

scrollProgress.js

function setProgress() {
    let bar = document.querySelector('.js-content-bar'),
            content = document.body,
            max = content.scrollHeight - window.innerHeight,
            progressValue = content.scrollTop / max * 100;

    bar.setAttribute('value', progressValue);
}

window.addEventListener('scroll', setProgress);
window.addEventListener('resize', setProgress);