Drop this cell into one of your Spark Notebook (https://github.com/andypetrella/spark-notebook/) declaring headings, execute, hide output, hide input

TOC.cell.js

:javascript
require(["jquery", "underscore"], function(j, _) {
  j(".toc").remove();
  var toc = j(document.createElement("div"));
  toc.attr("id", "toc")
     .addClass("toc")
     .css("position", "fixed")
     .css("top", "15%")
     .css("width", "8%")
     .addClass("panel").addClass("panel-info");
  
  var tocHeading = j(document.createElement("div")); 
  tocHeading.addClass("panel-heading")
            .appendTo(toc);
  var tocTitle = j(document.createElement("h5"));
  tocTitle.text("Table of Content")
          .appendTo(tocHeading);
  
  var tocBody = j(document.createElement("div")); 
  tocBody.addClass("panel-body")
         .appendTo(toc);
  
  var bodyContent = j(document.createElement("div"));
  bodyContent.css("max-height", "400px")
             .css("overflow", "auto")
             .css("max-width", "400px")
             .appendTo(tocBody);
  
  var notebook = j("#notebook");

  var current = 0;
  var ul, li;
  var container = bodyContent;
  j(notebook).find("h1,h2,h3").each(function(i, e) {
    var lvl = j(e).prop("tagName").substring(1)*1;
    if (current != lvl) {
      if (Math.min(current, lvl) == current) {
        current = lvl;
        var addUl = function(l) {
          var c = container;
          container = j(document.createElement("ul")).css("padding-left", "15px");
          container.addClass("lvl"+(current+l));
          c.append(container);
          if (l != 0) addUl(l-1);      
        }
        addUl(lvl-current);
      } else {
        container = container.parents(".lvl"+lvl);
        current = lvl;
      }
    }
    li = j(document.createElement("li")).html(j(e).html());
    var lk = li.find(".anchor-link");
    var href = lk.attr("href");
    lk.remove();
    var a = j(document.createElement("a")).html(li.html()).attr("href", href);
    li.empty();
    li.append(a)
    li.css("white-space", "nowrap")
    container.append(li);
  });

  toc.on(
    {
       "mouseenter": function() {j(this).css("width", "20%");},
       "mouseleave": function() {j(this).css("width", "8%");},
    }
  );
  
  toc.appendTo(j("body"));
  j('#toc').affix();
});