Change url on scrolling autoloaded articles

scroll-change-url.js

!function() {
    var wrap = document.querySelector('.tdb-autoload-wrap'),
        base = location.href;

    if (wrap) {
        window.addEventListener('scroll', function(e) {
            var wndTop    = window.scrollY,
                wndBottom = wndTop + window.innerHeight,
                wndHeight = window.innerHeight,
                currentArticle,
                currentFill;

            Array.prototype.forEach.call(wrap.children, function(article) {
                if (!currentArticle) {
                    currentArticle = article;
                    currentFill = 0.5;
                    return;
                }

                var artTop    = article.offsetTop,
                    artBottom = artTop + article.scrollHeight,
                    fill = (Math.min(artBottom, wndBottom) - Math.max(artTop, wndTop)) / wndHeight;

                if (fill > currentFill) {
                    currentArticle = article;
                    currentFill = fill;
                }
            });

            if (!wrap.currentArticle || currentArticle != wrap.currentArticle) {
                wrap.currentArticle = currentArticle;

                if (currentArticle.tagName.toLowerCase() == 'iframe') {
                    history.replaceState('', '', currentArticle.src.replace(/[\?&]tdb_action=tdb_ajax/, ''));
                } else {
                    history.replaceState('', '', base);
                }
            }
        });
    }
}();