# go-wasm-web — example app for the gowasm engine

A runnable example of kjol's **gowasm** engine: author UI **components in pure
Go**, compiled to **WebAssembly**, with **SSR + hydration**, **Next.js-style
server components**, layouts, and a **flash-free, state-preserving hot reload**.
No custom markup, no JSX — just Go. The engine lives in top-level kjol packages
(`kjol/go/{vdom,wasmruntime,rsc,wasmdevserver}`); this directory is only the app
that consumes them.

## Run it

```sh
cd cmd/examples/go-wasm-web
go run ./server            # codegen + SSR + hot reload at http://localhost:8085
```

Open http://localhost:8085. `/` and `/about` use the light **public** layout,
`/chart` and `/server` use the dark **app** layout. Edit any `.go` file and the
browser hot-swaps the new wasm **without a full reload or a flash**, preserving
page state; a build failure shows the Go compiler output as an overlay.

(`build.sh` does a one-off build instead of running the dev server.)

## This is a separate module

`go.mod` here declares its own module (`gowasmweb`) with `replace kjol => ../../..`,
so the app's `go-chart` dependency (and freetype / x/image) stays out of kjol —
the engine packages (`vdom`, `wasmruntime`, `rsc`, `wasmdevserver`) are
**stdlib-only**. `go build ./...` at the kjol root does not descend into this
nested module; build it from this directory.

## Layout

```
app/                the application — neutral, standalone functions (no central struct)
  pages.go            Deps + Shell + App/Public layouts + nav + Counter + pages
  chart.go            Chart page (go-chart, renders on both sides)
  server_counter.go   //gowasm:server component (server-only; clicks-over-time chart)
  *.gen.go            GENERATED by kjol/cmd/wasmgen (routes, layout dispatch, stubs)
wasm/               the js/wasm client entry point (main_native.go is a host stub)
server/             the dev-server main: injects Build/Render/Document into wasmdevserver
wwwroot/            bootstrap.js, bootstrap.min.css (+ generated wasm_exec.js, app.wasm)
```

## How it maps onto the engine (top-level `kjol` packages)

| Engine package | Role | This app's use |
|---|---|---|
| `kjol/vdom` | neutral virtual DOM (native + wasm): `VNode`, builders, `Signal`, `RenderHTML` | pages build `*VNode`; `server` SSRs with `vdom.RenderHTML` |
| `kjol/wasmruntime` | wasm client runtime: reconcile, `Run`/`Hydrate`, router, fetch, HMR state | `wasm/main.go` calls `Hydrate`/`Run` |
| `kjol/rsc` | stateless server components over HTTP (gob) | `//gowasm:server` + the generated client stub |
| `kjol/wasmdevserver` | reusable dev server: SSR, `/rsc`, hot reload, error overlay | `server/main.go` fills a `wasmdevserver.Config` |
| `kjol/cmd/wasmgen` | directive codegen → `app/*.gen.go` | run by `buildWasm` and `//go:generate` |

The **golden rule** holds: `wasmdevserver` imports no app code. The app injects
`Build` (how to compile the wasm), `Render` (SSR a route → HTML), and `Document`
(wrap it in a page) via `wasmdevserver.Config` — the same coupling inversion kjol
uses elsewhere.

## Directives (expanded by `wasmgen` at build time)

```go
//gowasm:page / static layout=public   // a route; `static` SSRs it, `layout=` wraps it
func HomePage(d Deps) func() *VNode { ... }

//gowasm:layout public                 // chrome for pages that opt into layout=public
func PublicLayout(d Deps, content *VNode) *VNode { ... }

//gowasm:server                        // runs on the server; calling it looks identical
func ServerCounter() func() *VNode { count := NewSignal(0); ... }
```