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I'm trying to ensure that visitors of my ASP.NET MVC website always have the most-current CSS and Javascript (and not some older cached version).

I tried to realize this by generating a seed value when the application domain starts, and automatically append it to the CSS and Javascript URLs (so now instead of /Content/All.js the link is /Content/All.js?549238 etc.).

Unfortunately I just found out by debugging via Firebug that this causes now a full download request every time (the new "seeded" response is no longer cached at all, but I only wanted the first check to download the 'updated' version, but then cache again/only check if there is a difference).

How can I achieve my goal, is there a better way of doing this? I need the client to always request the newest version, but then cache if no change happened.

Edit: This appears to be related to the fact that my page is served over SSL. I asked a follow up question here regarding enabling clientside caching with SSL.

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3 Answers 3

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Put the revision number in the url: foo.css?rev=348

-- Edit

You can achieve this pretty trivially as well, using your build tool (I actually do it with a custom thing I've written).

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And if it floats your boat, this is what SO does.

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I think the seed value you are generating is a random number. Replace this with a version number so that it will be re downloaded only when the version number of your application changes.

Like

/Content/All.js?appVer1.5

and when you modify the application you can change that to something like

/Content/All.js?appVer1.6

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It's not random. As I stated it's generated once as a static readonly when the application domain is initializing. Can't be written or changed more than exactly one single time for the entire lifetime of the w3wp process.
Accepted even though it didn't really answer my question... best/first though of the field.
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  1. Use a checksum of the file's content as the number, like All-a2a69e19d8628b65cb935708d64d7337.js. This way the number only changes when the contents of the script changes.

  2. Create some mechanism that is responsible for generating the link and/or <script> tag to the JavaScript file.

This way, in your ASP.NET page, have something like:

<asp:ScriptTag source="All.js"/>

Which gets replaced by:

<script src="/All-a2a69e19d8628b65cb935708d64d7337.js" type="text/javascript"></script>
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This is a little ridiculous. Why not just use the last modified date, if you're going to do with a scheme like this?
Because, to identify changes in the file, the modification time of the file is less accurate than its contents?
I don't think accuracy is a big matter in this situation.
No, the modification time will be quite accurate, unless you decide to programmatically change it to be back in time. Either way, it's not a good idea when it's so trivial to include the build number. Specially given you suggest changing the filename, which isn't required.

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