https://betterproposals.io/js/progress-bar-vertical.js?v=1.1

1// Timeline Scroll Section
2// --------------------------------------------------------------
3var items = $(".timeline li"),
4    timelineHeight = $(".timeline ul").height(),
5    greyLine = $('.default-line'),
6    lineToDraw = $('.draw-line');
7
8// Run this function only if draw line exists on the page
9if (lineToDraw.length) {
10  $(window).on('scroll', function () {
11
12    // Constants and dynamically calculated values
13    var greyLineHeight = greyLine.height(),
14        windowDistance = $(window).scrollTop(),
15        windowHeight = $(window).height() / 2,
16        timelineDistance = $(".timeline").offset().top;
17
18    // Calculate the position of the last checkpoint
19    var lastCheckpoint = $(".timeline li:last-child").offset().top;
20
21    // Max height for both lines
22    var maxHeight = lastCheckpoint - $(".timeline").offset().top;
23
24    // Update the draw-line height
25    if (windowDistance >= timelineDistance - windowHeight) {
26      var line = windowDistance - timelineDistance + windowHeight;
27
28      if (line <= greyLineHeight && line <= maxHeight) {
29        lineToDraw.css({
30          'height': line + 20 + 'px'
31        });
32      } else if (line > maxHeight) {
33        lineToDraw.css({
34          'height': maxHeight + 12 + 'px'
35        });
36      }
37    }
38
39    // Ensure the default-line ends at the last checkpoint
40    greyLine.css({
41      'height': maxHeight + 12 + 'px'
42    });
43
44    // Add the class 'in-view' to the visible li elements and 'dark-color' to their h2
45    var bottom = lineToDraw.offset().top + lineToDraw.outerHeight(true);
46    items.each(function () {
47      var circlePosition = $(this).offset(),
48          sectionH2 = $(this).find(".section-h2"); // Get the h2 inside this li
49
50      if (bottom > circlePosition.top) {
51        $(this).addClass('in-view');
52        sectionH2.addClass('dark-color'); // Add class to h2
53      } else {
54        $(this).removeClass('in-view');
55        sectionH2.removeClass('dark-color'); // Remove class from h2
56      }
57    });
58  });
59}