Playground — browser UI + Go backend #

A minimal end-to-end demo: a Go Cap'n Web server called from the browser with the reference capnweb client over WebSocket. It exercises the headline features of the protocol.

Run #

go run ./examples/playground
# open http://127.0.0.1:8088

No frontend build step — web/app.js is a native ES module that imports the capnweb client from a CDN (esm.sh), so an internet connection is needed the first time the page loads. The Go server serves the embedded UI and the WebSocket RPC endpoint at /ws.

What it shows #

• greet / add — plain RPC calls with typed arguments and return values.
• counter — NewCounter() returns a live server-side object by reference; each Increment() is a call on that remote stub, and its state lives on the server.
• pipelining — api.NewCounter().Add(10) pipes the counter promise straight into .Add without awaiting it, so both calls travel in a single round trip.

Layout #

• main.go — the Playground bootstrap service (Greet, Add, NewCounter), the Counter RpcTarget, and an HTTP server that embeds and serves web/.
• web/index.html, web/app.js — the browser UI (// @ts-check + JSDoc for editor type-checking without a compiler).