SourceForge Trac float diff format switcher with page scroll

trac-diff-float.js

// Set to autorun on sourceforge\.net\/.*/trac/.*/changeset/
(function ($) {
  var mods = $("#file-legend .mod + dd");
  if (mods.length == 0) return;
  
  var modsLen = parseInt(mods[0].textContent);
  if (!modsLen) return;
  
  // Cache diff dimensions.
  var tops = new Array(modsLen);
  var bottoms = new Array(modsLen);
  var switchers = new Array(modsLen);
  $("ul.entries li.entry").each(function (i, e) {
    var entry = $(e);
    var top = entry.offset().top;
    tops[i] = top;
    bottoms[i] = top + entry.height();
    switchers[i] = entry.find(".switch").first();
  });
  
  var fixstyle = $("<style>.switchfix { position: fixed; right: 23px; top: 5px; }</style>");
  fixstyle.appendTo("head");
  
  // Create page scroll detector.
  var scrolldet = $("<div class='scrolldet'></div>");
  scrolldet.css({
    position: 'fixed', right: '0px', top: '0px'
  });
  scrolldet.prependTo("body");
  
  $(window).scroll(function () {
    var pos = scrolldet.offset().top;
    for (var i = 0; i < modsLen; i++) {
      if (pos >= tops[i] && pos < bottoms[i])
        switchers[i].addClass("switchfix");
      else
        switchers[i].removeClass("switchfix");
    }
  });
})(jQuery);