main.js

    if ( $('body').hasClass('single-post') ) {
        window.addEventListener('scroll', function(e) {
            var s = (window.pageYOffset !== undefined) ? window.pageYOffset : (document.documentElement || document.body.parentNode || document.body).scrollTop;
            var body = document.body;
            var html = document.documentElement;
            var d = Math.max(body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight);
            var c = window.innerHeight;
            var position = (s / (d - c)) * 100;
            if ( $( "#atomion-progress-bar" ).length ) {
                $( "#atomion-progress-bar" ).css('width', position + '%');
            }
        });
    }