How can I force a hard refresh (ctrl+F5)?

Question

We are actively developing a website using .Net and MVC and our testers are having fits trying to get the latest stuff to test. Every time we modify the style sheet or external javascript files, testers need to do a hard refresh (ctrl+F5 in IE) in order to see the latest stuff.

Is it possible for me to force their browsers to get the latest version of these files instead of them relying on their cached versions? We're not doing any kind of special caching from IIS or anything.

Once this goes into production, it will be hard to tell clients that they need to hard refresh in order to see the latest changes.

Thanks!

Answer 1

You need to modify the names of the external files you refer to. For e.g. add the build number at the end of each file, like style-1423.css and make the numbering a part of your build automation so that the files and the references are deployed with a unique name each time.

Answer 2

What you might do is to call your JS file with a random string each time the page refresh. This way you are sure it's always fresh.

You just need to call it this way "/path/to/your/file.js?<random-number>"

Example: jquery-min-1.2.6.js?234266

Answer 3

In your references to CSS and Javascript files, append a version query string. Bump it everytime you update the file. This will be ignored by the web site, but web browsers will treat it as a new resource and re-load it.

For example:

<link href="../../Themes/Plain/style.css?v=1" rel="stylesheet" type="text/css" />
<script src="../../Scripts/site.js?v=1" type="text/javascript"></script>

Answer 4

Rather than a build number or random number, append the last-modified date of the file to the URL as querystring programmatically. This will prevent any accidents where you forget to modify the querystring manually, and will allow the browser to cache the file when it has not changed.

Example output could look like this:

<script src="../../Scripts/site.js?v=20090503114351" type="text/javascript"></script>

Answer 5

you could edit the http headers of the files to force the browsers to revalidate on each request

Answer 6

Since you mention only your testers complaining, Have you considered having them turn off their local browser cache, so that it checks every time for new content? It will slow their browsers a touch... but unless you are doing usability testing every time, this is probably a whole lot easier than postfixing the filename, adding a querystring param, or modifying the headers.

This works in 90% of the cases in our test environments.