How to detect expired user session in a react app?
There are two straightforward ways to deal with this issue in a React application that I can think of. Both inspired by a colleague of mine few days ago.
Use SSE (server-side-events) technology to PUSH notifications. As you correctly pointed out, this makes your API less pure. This approach should be quite an acceptable sacrifice where flawless UX is required AND/OR your server might need to push other notifications to the app.
Establish a short term timer somewhere in your client app (e.g.:
setTimeout(...)) that makes periodic calls to a "ping" API endpoint that will return current user/session information. This approach will impact UX for the duration of timeout, often negligible, and is commonly known as polling.
Hope this helps!
As an alternative to the naive polling, you can make it a little smarter by adding an endpoint that lets you know in how many seconds timeout is set to occur for the session at that point in time.
Then ping just before that time (instead of at a certain poll-rate) and update accordingly.
Logging out in another tab would return with an invalid token so would be picked up, too, but not as quickly if this is your main concern.
For this you could use broadcasting to let the other tabs know immediately (or use sessionStorage's change event to simulate a broadcast on unsupported browsers).
Otherwise the best way would be to implement a ServiceWorker; these can handle all requests for your app to the server. It's a centralised piece of code separate from your app that can broadcast to all tabs that a session is lost the moment it sees that one of its requests was rejected, and you can efficiently naively poll from this one place (instead of in each individual tab's runtime).