Including JavaScript Dynamically

If you have the desire to load JavaScript files dynamically and even know when they have loaded, this page is for you!

I wanted a way to make individual files for JavaScript classes and have them automatically load their parents without the web page having to know in advance all of the JavaScript includes that needed to be made.

I failed. But just for the class inheritance. I did write code that worked in the major browsers, which included JavaScript files dynamically. They also fired onload events so I could tell when everything was finally loaded. Don't worry, there are other solutions out there, such as RequireJS. Take a look at them if you need some serious on-demand loading of files.

I used a lot of information from Stoyan's blog to make the onload event work.

var jsIncludeFiles = [];

// Include a JavaScript file.  Functions like include_once per PHP.
function include(file) {
    var htmlElem = document.getElementsByTagName('head')[0];
    var js = document.createElement('script');

    js.setAttribute('language', 'JavaScript');
    js.setAttribute('type', 'text/javascript');
    js.setAttribute('src', file);

    // On Firefox, js.src is the fully qualified URL, IE it stays verbatim
    if (jsIncludeFiles[js.src]) {

    // IE
    js.onreadystatechange = function() {
        if (js.readyState == 'complete' || js.readyState == 'loaded') {

    if (js.addEventListener) {
        // Everything that supports the DOM2 event model
        // This should cover Firefox, Opera 9.2 and Safari
        js.addEventListener('load', includeDone, false);
    } else {
        // This may work for other browsers, such as older Mozilla-based
        // ones and perhaps older Safari versions
        js.onload = includeDone;

    jsIncludeFiles[js.src] = 'loading';


// Called when an include file has loaded
function includeDone(thisObj) {
    // IE will pass the script node, Firefox and others pass the Event.
    if ( {
        // Event was passed, pick out the script node
        thisObj =;
    if (jsIncludeFiles[thisObj.src]) {
        jsIncludeFiles[thisObj.src] = 'ready';
    if (! includeIsLoading()) {

function includeIsLoading() {
    for (var file in jsIncludeFiles) {
        if (jsIncludeFiles[file] == 'loading') {
            return true;
    return false;

This code is freely made available to everyone in case they can use it. It's under the MIT License.