This is a really small example that demonstrates ghcjs/jsaddle#64
To run:
cabal new-run
Then open http://localhost:8085/ in your browser and click the button.
On chrome it works fine. Under firefox it errors with:
Error : Unexpected Duplicate. syncCallbacks=True nBatch=2 nExpected=4
and the app spins sending many requests to jsaddle-warp.