Aeson is SLOOW compared to 'JSON.parse' + GHCJS ffi. You lose a bit of correctness (JSON.parse can decode numbers only to the JS precision, ie. 53bits, while Ae

Aeson is SLOOW compared to 'JSON.parse' + GHCJS ffi. You lose a bit of correctness (JSON.parse can decode numbers only to the JS precision, ie. 53bits, while Aeson supports arbitrary precision through Scientific), and ability to decode streams in constant memory. But these are features which you most likely don't need in a web app.