Today I saw a link to a script at called BuildTOC. The idea was actually a pretty good one but the implementation needed some work. The description of the script raised the first flag - “IE only”. After digging into the script to figure out why it was IE only I found the second flag. It was non-scemantic. The TOC was in one unordered list, no nesting, and the appearance of structure as provided by increased margins via CSS.

As you probably know it is best to separate presentation from content but the script was trying to use presentation to infer content. That works great if you can see - but if you can’t - then it seems like everything in the TOC is on the same level in the heirarchy.

So, intrigued by the script, but disappointed by it’s failings, I endeavoured to rewrite it. Here is my final version. (see a demo here):

var tocLevels = '6';

function tocInit(){
// because IE can't handle more than 6 levels; make sure the user hasn't
exceeded that amount
// if you remove this and use IE the script will no longer work if you have
invalid H7 tags and beyond.
if(tocLevels > 6){
tocLevels = 6;

var tags = '';
var tagNum = 0;
var tagDetail = new Array(1);
var tocTagList = '';
var aNode = '';

//Build a list of the header tags
for(var h=1;h<=tocLevels;h++){
tocTagList = tocTagList + 'H' + h + ',';

//create an array of those tags
var tocTagArray = tocTagList.split(',');

var tags = document.getElementsByTagName("body")[0].childNodes;

// loop over all objects on the webpage looking for valid header tags
for(var ti=0;ti<tags.length;ti++){
if (tocTagList.indexOf(tags[ti].tagName+',') != -1){

// this is used to buid the nested lists later
currentLevel = tocTagArray.find(tags[ti].tagName);

//build a unique anchor to embed with the section header
aNode = document.createElement('a'); = 'tocLink'+tagNum;

// collect some details about the section that we can use to build the TOC
tagDetail[tagNum] = tags[ti].tagName + '|' + tagNum + '|';
tagDetail[tagNum] = tagDetail[tagNum] + tags[ti].childNodes[0].nodeValue + '|'
+ currentLevel;
} else {
tagDetail[tagNum] = tagDetail[tagNum] + ' ' + '|' + currentLevel;

tagNum++; // used to keep track of how many headers we have found.



function tocBuild(tagDetail){

var lastLevelNum = -1;
var currentLevelNum = 0;
var toc = getObjectRefByID('TOC');
var currentParent = toc;
var lastObject = currentParent;

for(var i = 0; i < tagDetail.length; i++) {
thisDetail = tagDetail[i].split("|");

currentLevelNum = thisDetail[3];

// created a nested unordered list..
if(currentLevelNum > lastLevelNum){
var ulNode = document.createElement("ul");
currentParent = ulNode;
//move back up the DOM to the right level
if(currentLevelNum < lastLevelNum){
var levelDiff = lastLevelNum - currentLevelNum;
currentParent = currentParent.parentNode;

//add the new TOC entry
var liNode = tocBuildEntry(thisDetail);

//keep track of where we are
lastLevelNum = currentLevelNum;
lastObject = liNode;


function tocBuildEntry(details){

var liNode = document.createElement("li");
var aNode = document.createElement("a");
var tNode = document.createTextNode(details[2]);

// className is the same as the tag, ie: H1, H2, etc.
liNode.className = details[0];
aNode.className = details[0];

//embed a link in the LI so we can jump to the correct section
aNode.href = '#tocLink'+details[1];

return liNode;


function addEvent(elm, evType, fn, useCapture)
// addEvent and removeEvent
// cross-browser event handling for IE5+, NS6 and Mozilla
// By Scott Andrew
if (elm.addEventListener){
elm.addEventListener(evType, fn, useCapture);
return true;
} else if (elm.attachEvent){
var r = elm.attachEvent("on"+evType, fn);
return r;
} else {
alert("Handler could not be removed");

function getObjectRefByID(objectId) {
var element = false;

// cross-browser function to get an object given its id
if(document.getElementById && document.getElementById(objectId)) {
// W3C DOM
element = document.getElementById(objectId);
else if (document.all && document.all(objectId)) {
element = document.all(objectId);
else if (document.layers && document.layers[objectId]) {
// NN 4 DOM.. note: this won't find nested layers
element = document.layers[objectId];

return element;

Array.prototype.find= null;
if(!Array.prototype.find) {
function ArrayFind(value){
// simply add the element to the end of the array changing the arrays
// length by +1
var index = -1;
for(var i=0; i<this.length;i++){
if(this[i] == value){
index = i;
return index;
// set the Arrays push method equal to our ArrayPush function
Array.prototype.find = ArrayFind;

// builds the TOC when the page is loaded.
addEvent(window, "load", tocInit);



lol! thanks

Jeff Coughlin

Ahh. I get it :)

I think we are all plagued as developers to clean up code when we see poorly designed (or implimented) code. (Zombie voice, “Must clean code”).

Good job then :)


that’s what my version of the script does and is one of the things I did to improve the version I saw at

this script is purely meant as an exercise to fix the faults of the other script.

1. works in DOM compliant browsers 2. builds a nested unordered list to provide structure

Jeff Coughlin

Why not make it a nested unordered list and use CSS to display it properly (which should work in IE as well as other browsers)?

This will separate content from logic and will eliminate the need for javascript.

[ul] --[li]Topic 1.0 -—[ul] -—–[li]Topic 1.1[/li] -—–[li]Topic 1.2[/li] -—[/ul] --[/li] --[li]Topic 2.0[/li] [/ul]