Bundling and minification ASP.NET

Question

I have a huge web application that bundles and minifies a huge amount of javascript and css files.

When we release a new version, we notice that at the first request of each page (controller + view) the software takes a lot of time to respond. So, I started to search a little bit and find out Bundle Caching and it seems when some .js or .css files are changed, the bundle will create a new token. But I have some doubts about it:

1. When exactly the join and minification of the files is made? It is when it is called at the first time on a view?
2. There is a possibility that when the software is build, the files will be joined and minified during that process, so when at the first time the virtual path is called, this process already had occurred and cached?
3. If the slowly problem about my application is not the bundling and minification of the files, what could be?

Thank you.

Note: I'm talking about the process in a production environment. So, thinks like putting debug=false in the web.config I already have.

Answer 1

1) I would not bet on this one, but I am pretty sure that this needs to be done upfront provided that the version of the bundle is appended to the path as a query string parameter. Since this value is the hash of the bundle result, this needs to be done before any bundle can be downloaded in order for ASP.NET to even be able to add this parameter when you do something like this:

@Url.Content("~/bundles/yourbundle")

Whether it is calculated the first time the bundle url is rendered into the view or at app startup is something I don't know. I still post this answer because I believe I can give you useful information for the 2) and 3) points.

2) It is possible to bundle your files beforehand. You can either use some Gulp or Grunt task, use the Bundler & Minifier extension, or any tool of your preference. In that case, however, you are not required (or even advised¹) to use virtual paths as these tools produce physical files. However, you will need to make sure yourself that they are versioned properly so whenever you change some input file, the clients will be forced to download the new one instead of using the one in their cache.

3) Keep in mind that C# is not compiled to machine code. Initial slowness can, and usually is, caused by something called JITting (which is explained in greater detail here), that is, the process of transforming the IL code into machine code. This is a rather lazy process in that it basically happens just before the actual execution of your code. If, for example, you have a method A, it does not get transformed to machine code up until it is actually invoked. Therefore, the first access of every controller/action is slower than subsequent ones (because after the first run, the resulting machine code is kept).

You can also configure your project to compile your views which will cause your app to be slightly faster at the cost of making the build process slower.

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¹ It is advisable to use physical paths if the files are actually physically present on the disk because like that, you can skip the virtual path resolving process altogether thus making script loading to be a little bit faster.

Answer 2

Bundling and minification is enabled or disabled by setting the value of the debug attribute in the compilation Element in the Web.config file. In the following XML, debug is set to true so bundling and minification is disabled.+ XML

<system.web>
    <compilation debug="true" />
    <!-- Lines removed for clarity. -->
</system.web>

To enable bundling and minification, set the debug value to "false". You can override the Web.config setting with the EnableOptimizations property on the BundleTable class. The following code enables bundling and minification and overrides any setting in the Web.config file. C#

public static void RegisterBundles(BundleCollection bundles)
{
    bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
                 "~/Scripts/jquery-{version}.js"));

    // Code removed for clarity.
    BundleTable.EnableOptimizations = true;
}

Unless EnableOptimizations is true or the debug attribute in the compilation Element in the Web.config file is set to false, files will not be bundled or minified. Additionally, the .min version of files will not be used, the full debug versions will be selected. EnableOptimizations overrides the debug attribute in the compilation Element in the Web.config file