API Reference

lamassu-js has two embedding surfaces, plus a command-line tool:

• npm package — @mdy-docs/lamassu-js, the engine compiled to a WebAssembly ES module with a small JS wrapper. Use this from Node or the browser.
• C embedding API — the native liblamassu C library (include/lamassu.h and include/lamassu_compile.h), for embedders working directly in C, or building their own bindings for another host environment.
• The lamassu CLI — see below.

All three sit on top of the same core: a portable C11 interpreter with no static globals — every function takes a JsVm or JsContext handle explicitly, so multiple independent engine instances can coexist in one process. The npm package is a thin Emscripten-compiled wrapper around exactly this C API; if you're embedding from C directly, the C embedding API page is the ground truth.

See Async & host calls for how the two embedding surfaces relate on the async side: the npm package's __hostcall is a synchronous-looking guest call built on Emscripten Asyncify (it suspends the whole WASM call stack), while the C API's js_promise_new/js_resolve/js_run_jobs is the lower-level, host-neutral mechanism behind ordinary guest-level await of a native-returned promise — two complementary mechanisms, not one built on the other.

Whichever you pick, the sandbox limits are off until you set them. Running untrusted code covers all three.

The lamassu CLI

make cli builds build/lamassu, which runs a source file, a bytecode cache, or an interactive REPL — the same library, driven from a shell. The wasip2 build shares the file, so it takes the same options.

lamassu [options] [file.js]             # run a source file, or the REPL
lamassu [options] --run-bytecode FILE   # run a bytecode cache
lamassu --emit-bytecode SRC OUT         # compile SRC to a bytecode cache

option	meaning
--fuel N	Bytecode-instruction budget per evaluation (0 = unlimited). Roughly 3e8 per second.
--heap-limit N	Cap on the guest heap, with an optional K/M/G suffix (e.g. 64M).
-h, --help	The same summary, from the tool itself.

Options come before the subcommand or filename. Both limits are off by default, which is what you want for your own code and not what you want for anyone else's; the budget is armed per evaluation, so a REPL survives while (true) {} and keeps going. Neither bounds wall-clock on its own — see Running untrusted code.