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fluffos/docs/efun/jsbridge/js_eval.md
Yucong Sun e6f0c377f8
wasm: run the full driver in the browser (Emscripten port) (#1231) 
The driver cross-compiles to WebAssembly and runs a complete mudlib
inside a webpage: compiler, VM, all portable efun packages, and the
real telnet protocol layer -- the page is the telnet client, JavaScript
is the wire. The LPC testsuite passes inside the wasm driver (browser
and node).

Architecture (src/wasm/README.md):
- Transport interface (src/net/transport.h): each interactive_t owns an
  abstract byte pipe (write/flush/schedule_command/close). comm.cc and
  telnet.cc are transport-agnostic and compile unchanged on every
  target. Implementations select at link time: SocketTransport +
  WebsocketTransport (net/transport_libevent.cc, native) vs
  WasmConsoleTransport (src/wasm/comm_wasm.cc).
- Inverted event loop: the shared gametick/event core stays in
  backend.cc; backend_libevent.cc (blocking loop) vs
  src/wasm/backend_wasm.cc (page-driven fluffos_tick(now_ms), walltime
  priority queue, capped catch-up). Other per-target singletons (TLS,
  DNS resolver, crash handler) follow the same link-time pattern -- no
  #ifdef __EMSCRIPTEN__ in shared logic files.
- Mudlib rides in Emscripten's MEMFS via file_packager; driver file I/O
  needed zero changes.

jsbridge package (WASM only): js_eval() (sync), js_call() (async page
handlers with LPC callbacks), js_export() (page calls LPC via
Module.fluffos.callLPC, Promise-resolved on a later tick) -- fetch,
canvas/WebGL, storage, page UIs driving the game. Demo in
testsuite/command/jsdemo.lpc + the bundled web terminal.

Build/tooling: native-tools + wasm CMake presets (host codegen tools,
then cross build); tools/wasm/build-deps.sh (ICU + zlib cross-builds,
including the ICU genccode data quirk); tools/wasm/pack-mudlib.sh
(any mudlib + driver -> static web bundle, also works standalone from
the release zip); src/www/wasm/index.html (self-contained web terminal
with a minimal telnet client). On emsdk >= 3.1.57 the build uses native
wasm exceptions (-fwasm-exceptions); older toolchains fall back to
-sDISABLE_EXCEPTION_CATCHING=0.

CI/release: a wasm CI job (latest emsdk, deps cache keyed on resolved
emcc version) gates PRs on the LPC testsuite running inside the wasm
driver under node; release.yml ships fluffos-<version>-wasm.zip
(driver + web terminal + pack-mudlib.sh). Fixed a stale-predefine bug:
options.autogen.h now depends on packages.autogen.h + config.h.

Docs: docs/build-wasm.md (end-to-end workflow), docs/driver/wasm.md
(packer + jsbridge cookbook), docs/efun/jsbridge/*, README + AGENTS
updated. Testsuite files for optional packages guard themselves with
#ifdef __PACKAGE_*__.


Claude-Session: https://claude.ai/code/session_01VVpphH3cgXyziRDCbjUVkb

Co-authored-by: Claude <noreply@anthropic.com>
2026-07-10 23:33:51 -04:00

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title
jsbridge / js_eval

js_eval

NAME

js_eval - evaluate JavaScript in the hosting page, synchronously

SYNOPSIS

string js_eval(string code);

DESCRIPTION

Evaluates `code` as JavaScript in the context of the page (or node
process) hosting the WASM driver and returns the result as a string:
primitives are stringified, objects are JSON-encoded, undefined/null
become "". A thrown JavaScript exception is returned as the string
"JS error: ..." — it never unwinds into the driver.

Only available on the WebAssembly build (guard LPC code with
`#ifdef __PACKAGE_JSBRIDGE__`).

EXAMPLES

```c
write(js_eval("navigator.userAgent"));
int width = to_int(js_eval("window.innerWidth"));
```

SEE ALSO

js_call(3)

NOTE

A page can disable eval entirely with a Content-Security-Policy; use
js_call(3) with page-registered handlers for anything structural.