HCL Domino Ideas Portal
Welcome to the #dominoforever Product Ideas Forum! The place where you can submit product ideas and enhancement request. We encourage you to participate by voting on, commenting on, and creating new ideas. All new ideas will be evaluated by HCL Product Management & Engineering teams, and the next steps will be communicated. While not all submitted ideas will be executed upon, community feedback will play a key role in influencing which ideas are and when they will be implemented.
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You could implement a SessionListener on the server side, which would at least signal to you when a given HTTP session with the server has timed out - that may do what you want.
The browser does not allow to act on the event of closing a browser window. It's just gone and there is nothing that XPages can do about it.