pdfkit/docs/js/scroll.js

$(function() {
  $('pre code').addClass('hljs coffeescript');
  hljs.initHighlightingOnLoad();
    
  var sections = $("h2[id]");
  window.onhashchange = function() {
    $("a.selected").removeClass("selected");
    $("a[href=" + location.hash + "]").addClass('selected');
  }
  
  $(window).bind("mousewheel DOMMouseScroll", function() {
    var scrollTop = $(window).scrollTop() + document.documentElement.clientHeight / 3,
        section = null,
        link = null;
        
    for (var i = 0, len = sections.length; i < len; i++) {
      var top = sections.eq(i).offset().top;
          
      if (i < len - 1) {
        var nextTop = sections.eq(i + 1).offset().top;
        if (scrollTop > top && scrollTop < nextTop) {
          section = sections[i].id;
          break;
        }
      }
    }
    
    if (!section) {
      section = sections[len - 1].id;
    }
    
    link = $("a[href$=#" + section + "]");
    if (!link.hasClass('selected')) {
      $("a.selected").removeClass('selected');
      link.addClass('selected');
    }
  });
});