[deno]

Protocol Buffers can even serialize down to JSON (as does Thrift, for example).

Client code for PB+JSON has been a part of Google’s Closure library in fact (open source), and they used it in production for Gmail’s RPC, but I’m not sure if it’s still supported/recommended for PB 3.

The reason to use JSON instead of compact binary representation has been because JSON.parse is fast and doesn’t require any additional code. But nowadays JS is fast enough in most cases (unlike you’re doing something like streaming with media exts), but you can also ship Web Assembly/NACL library and (soon) delegate parsing to Web Worker with shared memory which should altogether give best possible performance.