UmbracoStartUpHandler.cs

    public class SiteStartupHandler : IApplicationEventHandler
    {
        public void OnApplicationStarted(UmbracoApplicationBase umbracoApplication,ApplicationContext applicationContext)
        {
            // Register bunding for umbraco
            RegisterStyles(BundleTable.Bundles);
            RegisterJavascript(BundleTable.Bundles);
        }
        private static void RegisterStyles(BundleCollection bundles)
        {
            //Add all style files. These will be bundled and minified.
            //After everything has been bundled (which only happens when debug=false in the web.config) check if there are no errors in the bundled file. Not all files can be bundled.
            bundles.Add(new StyleBundle("~/bundle/site.css").Include(
                    "~/content/style.css"
                )
            );
        }

        private static void RegisterJavascript(BundleCollection bundles)
        {
            //Add all javascript files. These will be bundled and minified.
            //After everything has been bundled (which only happens when debug=false in the web.config) check if there are no errors in the bundled file. Not all files can be bundled.
            bundles.Add(new ScriptBundle("~/bundle/site.js").Include(
                    "~/scripts/example.js"
                )
            );
        }
}