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Web cache behavior of Office add-ins

Manuel Sidler 5 Reputation points
2024-03-06T12:48:33.17+00:00

We use meta tags to disable caching for the index.html file of our Office add-in:

<!doctype html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <link rel="icon" href="/favicon.ico" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate">
        <meta http-equiv="Pragma" content="no-cache">
        <meta http-equiv="Expires" content="0">
        <title>Sample Add-In</title>
    </head>
    <body>
        ...
    </body>
</html>

This works fine in most cases. But there are some rare occasions where Office caches the index.html file, despite of the meta tags. Closing and opening the add-in doesn't load the current version. Right click -> reload does load the current version, but after closing and opening the user gets the old cached version again. To force Office loading the current version, the user has to clear the web cache.

It's not clear how and when Office does cache the index.html file and why the caching meta tags get ignored sometimes?

Microsoft 365 and Office | Development | Other

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