ASP.NET Bundling - Bundle not updating after included file has changed (returns 304 not modified)

I am trying out ASP.NET Bundling with ASP.NET MVC 4 application. The situation is that I want to make a CDN style service, which has JS and CSS files to which you can address from other sites with this type address: http://www.mycdn.com/scripts/plugin/js, which bundles and minifies all included .js files.

My bundle config for one file looks like this:

bundles.Add(new ScriptBundle("~/Scripts/plugin/pluginjs").Include("~/Scripts/plugin/jquery.plugin.js"));

However, when I do this, the bundles are not getting updated even after I change the original js files. I keep on getting 304 Not Modified, when I refresh my browser, and the content of the minified file is not updated. How can I make bundles update, because it is useless to have bundles with old content? I tried out every way, but could not figure out a solution.

Thanks in advance!

I just had the exact same problem. I have a folder with 2 CSS files:

• ~/Content/main.css
• ~/Content/main.min.css (pre-existing from my previous manual minification process)

My bundling code is this:

bundles.Add(new StyleBundle("~/css/main").Include("~/content/main.css"));

No matter how much I changed my main.css the output was the same url with the same contents:

<link href="/css/main?v=6Xf_QaUMSlzHbXralZP7Msq1EiLTd7g1vId6Vcy8NJM1" rel="stylesheet"/>

The only way to update the bundle was to rebuild my solution - obviously not the best approach.

However as soon as I deleted main.min.css, everything started to work just fine. Playing a little more I discovered that if there are both main.css and main.min.css, then updating main.min.css will actually update the bundle... Weirdness, but at least predictable.

After fighting to figure out what makes the bundle cache refresh I came to a few conclusions that will hopefully help others:

If .min files ARE included as part of the bundle:

• release mode + change min js code = cache refresh
• release mode + change non min js code = no cache refresh
• debug mode + change min js code = no cache refresh
• debug mode + change non min js code = no cache refresh

If .min files are NOT included as part of the bundle:

• debug mode + change js code = no cache refresh
• release mode + change js code = cache refresh

Notes

• By debug mode i mean web.config compilation debug = true (and BundleTable.EnableOptimizations = false or is omitted)
• By release mode i mean web.config compilation debug = false (and BundleTable.EnableOptimizations = true or is omitted
• Be sure you are actually making code changes. Changes such as spaces and comments do not affect the resulting minified js so the server is correct in that there are no changes (so the bundle cache is not refreshed).

Please note that if you are using Google Chrome the caching is quite aggressive. To ensure nothing is cached, you can do Ctrl-Shift-I to bring up the developer pane. Go to Network and click Disable Cache. Ensure you keep this open. Now refresh the page. Your cache should be cleared and the file changes should be reflected now.

Okay, here's my story. I disabled generation of min files for less files in Web Essentials. Old min files were not deleted, and bundle thingy saw those instead of updated CSS. Good luck!

EDIT

Sometime later I spent another good 2 hours on the same issue. This time it was my fault I guess - I forgot the leading tilde, i.e. I wrote

Scripts.Render("/js/script")

in lieu of

Scripts.Render("~/js/script")

For whatever reason it sometimes worked, and sometimes it did no such thing.

I actually decided to not to use System.Web.Optimization for this task, but I found Microsoft Ajax Minifier, which is also included in WebGrease.dll, which comes with MVC4 System.Web.Optimization library. I wrote the following function, which I then called in Application_Start for each minified file:

    public static void MinifyFile(string virtualPath)
    {
        string fullPath = HttpContext.Current.Server.MapPath(virtualPath);
        string extension = Path.GetExtension(fullPath).ToLower();
        string targetPath = fullPath.Substring(0, fullPath.Length - extension.Length) + ".min" + extension;
        if(File.Exists(fullPath) == false) 
        {
            throw new FileNotFoundException("File not found: " + fullPath);
        }
        string input = File.ReadAllText(fullPath);
        string output;
        if (extension == ".js")
        {
            Microsoft.Ajax.Utilities.Minifier jsmin = new Microsoft.Ajax.Utilities.Minifier();
            output = jsmin.MinifyJavaScript(input);
        }
        else if (extension == ".css")
        {
            Microsoft.Ajax.Utilities.Minifier jsmin = new Microsoft.Ajax.Utilities.Minifier();
            output = jsmin.MinifyStyleSheet(input);                
        }
        else
        {
            throw new NotSupportedException(extension + " is not supported for minification.");
        }
        File.WriteAllText(targetPath, output);
    }

Now, my application is minifying all files on Application_Start.

The bundling operation is case sensitive. Make sure the filename has the proper case.

I had to change a line in my BundleConfig.cs:

bundles.Add(new StyleBundle("~/Content/css").Include(
    "~/Content/bootstrap.css",
    "~/Content/Site.css"));  <-- Uppercased.

I'm not sure the feature as it currently stands will really support being a CDN, as it relies implicitly on the url to contain a hashcode to prevent browser caching.

But I can try to help you try to get there, and maybe its possible today... One issue that might potentially be a roadblock is that the BundleHandler will return 304 on any bundle requests that contain the IfLastModified header, since the assumption is that the browser cache is always valid due to the fingerprint in the url.

Can you add some details about how you are rendering references to the bundles? Are you using something like Scripts.Render("~/Scripts/plugin/pluginjs")?

Your bundle script tag should look something like this:

Good: <script src="/fbt/bundles/js?v=wvLq7H7qEZB2giyIRn7aEZAxhHOb2RfTYYh2HMd9EqM1"></script>

If your script tags are referencing the raw bundle with no version string, that would likely explain the caching issues you are seeing:

Not good: <script src="/fbt/bundles/js></script>

I know its been a while since this was updated but I have found I just need to wait a couple seconds to let the bundle catch up with my css changes. I have the bootstrap less files being compiled into a css and min.css and its definitely not instant to see my changes. For me it was about 10 seconds on a fast pc with an ssd. Your miles may vary based on your system specs.

I saw this answer but none of these were the case for me. There were certain CSS rules that were making the styles bundler fail and i was getting the same hash, even if i made changes to the CSS file. It was all working correctly before for me.

In my case the violating css selector rule was -

#globalSearch.searching { ... }

If i made this just

.searching { ... }

It all starts working again and any changes i make to my css file the bundler hash changes correctly. Just adding this answer as it might help someone.

Just update your System.Web.Optimization by NuGet

For what it's worth, I had the same problem just now with one js file inexplicably refusing to update no matter what (rebuild, forced cache clear etc). After a while, I switched the client debug tools in IE on (F12) to start watching the network traffic, and this act alone forced the JS file to refresh. Go figure, but it worked.

The Issue for me was I had Fiddler running. After I close dit and rebuilt my solution it was loading the changes in the js file for me.

I had a similar problem. In my situation, I had a CSS file referenced in a style bundle and had that bundle referenced in my MVC view. I also had the "EnableOptimizations" flag set to false in the bundle code.

Despite all this, the view refused to update to include the new CSS file.

My solution was to create a minified version of the CSS file and include it in the project and it started working. I have no idea why this would be the case since that minified file is not referenced anywhere (even after the view updated) and shouldn't even be considered since the code is set to not be optimized. This is most likely a bug (or a feature) of the bundling functionality. I hope this helps someone else running into this problem.

Make sure your app is really being deployed in Release mode and that your host is fiddling with settings. I was having this issue, but after investigating, I realized my files were not actually being bundled. I was deploying in Release mode, but for some reason (I suspect host), I think my app was really deployed in debug.

I had to set the following at the end of the BundleConfig.cs file to force bundling, which in turn forced the updated file to finally show in the browser.

BundleTable.EnableOptimizations = true;

I had this issue today and I went through all the answers but my problem wasn't solved by any of the solutions here. Later I found that this was happening because there was an error in my CSS. One of the urls was not closed (the last single quote was missing).

This caused the css file to have a syntax error and it didn't compile for the Bundleconfig. I suppose there would have been a message in the Output log, but I hadn't checked.

If this is happening to you in 2020, try making sure your CSS does not have a syntax error.