Force clients to refresh JS/CSS files

Force clients to refresh JS/CSS files

It's a common problem with an easy solution. You make some changes to a JavaScript of CSS file, but your users still report an issue due to the old version being cached.

You could wait for the browsers cache to expire, but that isn't a great solution. Worse if they have the old version of one file and the new version of another, there could be compatibility issues.

The solution is simple, just add a querystring value so that it looks like a different path and the browser downloads the new version.

Manually updating that path is a bit annoying though so we use modified time from the actual file to add the number of ticks to the querystring.


1using Utilities;
2using UrlHelper = System.Web.Mvc.UrlHelper;
4namespace Web.Mvc.Utils
6 public static class UrlHelperExtensions
7 {
8 public static string FingerprintedContent(this UrlHelper helper, string contentPath)
9 {
10 return FileUtils.Fingerprint(helper.Content(contentPath));
11 }
12 }


1using System;
2using System.IO;
3using System.Web;
4using System.Web.Caching;
5using System.Web.Hosting;
7namespace Utilities
9 public class FileUtils
10 {
11 public static string Fingerprint(string contentPath)
12 {
13 if (HttpRuntime.Cache[contentPath] == null)
14 {
15 string filePath = HostingEnvironment.MapPath(contentPath);
17 DateTime date = File.GetLastWriteTime(filePath);
19 string result = (contentPath += "?v=" + date.Ticks).TrimEnd('0');
20 HttpRuntime.Cache.Insert(contentPath, result, new CacheDependency(filePath));
21 }
23 return HttpRuntime.Cache[contentPath] as string;
24 }
25 }