Have you seen Facebook's Flux/Dispatcher framework, for example? The Dispatcher is usually a massive switch statement that takes a single argument, which will be a record field that corresponds with the event type. It's exactly like switching on uMsg and then casting lParam to the relevant struct. And this is considered one of the absolute best web frameworks available right now.
On the bright side, I suppose we can look forward to equivalents of message crackers, OWL, and MFC for React soon enough.