Reference:Updating Applets

You may have some applets on your website that are no longer visible because they are using Java technology which is not supported by browsers anymore. You have two options to update them.

Uploading to GeoGebra

Take the original GeoGebra files, them to GeoGebra and save the activity. Go to Details > Share > Embed and replace the applet on your site with the embed code. Advantage of this method is that you get nice preview images, we suggest to do this if you only have a few applets.

Updating Applets with a Script

Add the following snippet to the source of your webpage (preferably just above </body>):

<script src="https://cdn.geogebra.org/apps/rebootggb.js" type="text/javascript"></script>

When a user views your webpage, this script will replace all the Java applets with HTML5 ones. This method is suitable if you need to quickly update a large amount of applets.

Viewing Applets on Other Websites

In case you want to view applets on someone else's website, you can use a bookmarklet.