gRPC as specced to ride directly on top of HTTP/2 doesn't work from browsers, the sandboxed JS isn't allowed that level of control over the protocol. And often

gRPC as specced to ride directly on top of HTTP/2 doesn't work from browsers, the sandboxed JS isn't allowed that level of control over the protocol. And often is too low level to implement as part of a pre-existing HTTP server, too. gRPC is a server-to-server protocol that is not part of the usual Web, but happens to repurpose HTTP/2. Outside of gRPC, just HTTP POST cannot at this time replace websockets because the in-browser `fetch` API doesn't support streaming request body. For now, websockets is the only thing that can natively provide an ordered stream of messages from browser to server.