Dynamically load JavaScript files with callback when finished

javascript_loader.js

// Example:
Loader.load("/script/main.js");

Loader.load(base_url + '/include/fancybox2/jquery.fancybox.pack.js', function() {
    $('.fancybox').fancybox();
});

var Loader = {
    load: function(src, callback) {
        var script = document.createElement('script'),
        loaded;
        script.setAttribute('src', src);
        if (callback) {
            script.onreadystatechange = script.onload = function() {
                if (!loaded) {
                    callback();
                }
                loaded = true;
            };
        }
        document.getElementsByTagName('body')[0].appendChild(script);
    }
};