clicking logout twice brings "TypeError: Failed to fetch"

[HonkXL]

Users sometimes doing double clicks in webpages or sometimes the loading needs too long time.
When clicking twice to Logoff, there will come: TypeError: Failed to fetch.

Would be great to modify logout to handle this smoother.

[BertKoor]

I don't think this can be fixed. Official documentation on this error:
https://storage.googleapis.com/chatgpt-blog-proto-proxima/blog/typeerror-failed-to-fetch.html

None of the listed causes seem to apply here.

I've looked at server logging, double-checked by debugging the code and what I see is that at the server side (webtrees code we have influence on) the POST request to log out is handled twice: first request is normal, during the second request it concludes the user is already logged out and then basically does nothing but send a redirect to the home page. That last response seems only to be received by the browser when the user refreshes the page.

If nothing at server-side can be done, then the only possiblilty is at client-side: hold state in JavaScript whether the user is logged in. My gut feeling is that this makes the code far more complex than nescessary and even might introduce the risk that deadlocks occur or users cannot log out because a JavaScript variable or browser cookie happens to have the wrong value at the wrong time. Handling race conditions like this is one of the most difficult things. In my experience it never helps to try and fight it by adding more complexity.