Set asp-append-version True by Default for JavaScript, & CSS to the Bust Cache

When I add a JavaScript file or CSS file in .NET, I want asp-append-version set to true 99.9% of the time. This way I don't have to tell users or testers to clear their cache if I update those files. You can do this with your web server settings as well but I prefer it if my application does it at build time.

I reached out via the GitHub repository where the .NET team does an awesome job of replying & working with community members in my experience. Damian Edwards replied with a great solution. Damian's solution uses Tag Helpers.

With Tag Helpers, instead of saying <script src="~/js/site.js"></script> you would write <script asp-src-include="~/js/site.js"></script>.

.NET 6 Version

If you launch a new .NET 6 Web app, your program.cs file will look like this at the top.

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

After the AddRazorPages() method we can add custom helpers.

builder.Services.AddSingleton<ITagHelperInitializer<ScriptTagHelper>, AppendVersionTagHelperInitializer>();
builder.Services.AddSingleton<ITagHelperInitializer<LinkTagHelper>, AppendVersionTagHelperInitializer>();

Then create a AppendVersionTagHelperInitializer class somewhere in your project. Here's Damian's version which sets AppendVersion = true by default.

public class AppendVersionTagHelperInitializer :
    private const bool DefaultValue = true;

    public void Initialize(ScriptTagHelper helper, ViewContext context)
        helper.AppendVersion = DefaultValue;

    public void Initialize(LinkTagHelper helper, ViewContext context)
        helper.AppendVersion = DefaultValue;

Now when you add JavaScript with <script asp-src-include="~/js/site.js"></script> or CSS with <link rel="stylesheet" asp-href-include="~/css/site.css" /> it will add a ?v{Hash} after it <script src="/js/site.js?v=dLGP40S79Xnx6GqUthRF6NWvjvhQ1nOvdVSwaNcgG18"></script>.

.NET 3 Version

For slightly older .NET projects, the only thing that changes is instead of using program.cs to add our singletons we do it in startup.cs like this:

public void ConfigureServices(IServiceCollection services)
    services.AddSingleton<ITagHelperInitializer<ScriptTagHelper>, AppendVersionTagHelperInitializer>();
    services.AddSingleton<ITagHelperInitializer<LinkTagHelper>, AppendVersionTagHelperInitializer>();

Creating Tag Helpers

You can take this further by creating your own tag helpers. The .NET docs have a good e-mail example.

One Last Thing...

If you have a question or see a mistake, please comment below.

If you found this post helpful, please share it with others. It's the best thanks I can ask for & it gives me momentum to keep writing!

Matt Ferderer
Software Developer focused on making great user experiences. I enjoy learning, sharing & helping others make amazing things.
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