ASP.NET bundling and minification. Runs once per request?

Question

I am wondering how may times the bundling and minification runs on the server?

Is it once per HTML request? Once per browser session? Once every time the app gets deployed?

Answer 1

Bundles are created when the application is deployed or restarted, when the Application_Start method is called in Global.asax.cs. Inside Application_Start, BundleConfig.RegisterBundles is invoked, which is actually where the magic happens.

public class MvcApplication : System.Web.HttpApplication
{
    // this method is called on application start
    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas(); // registers areas
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); // registers filters
        RouteConfig.RegisterRoutes(RouteTable.Routes); // registers routes
        BundleConfig.RegisterBundles(BundleTable.Bundles); // this generates the bundles
    }
}

And in your BundleConfig.cs file, the RegisterBundles method is the method that is called to create said bundles.

public class BundleConfig
{
    public static void RegisterBundles(BundleCollection bundles)
    {
        // this is actually what's creating the bundles
        bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
                    "~/Scripts/jquery-{version}.js"));
        // etc...
    }
}

They are then cached in memory, can be accessed at /bundles/bundlename?v=versionId, and served for each HTTP request, but the actual process of bundling and minification only happens once.

Answer 2

bundling and minification registered with Application_Start runs once and result is cached on server. Cached version provides for other request. Aplication_Start fires when first resource requested.