Show HN: QuickBEAM – run JavaScript as supervised Erlang/OTP processes (opens in new tab)

2. No. JS runs on a dedicated OS thread, outside the BEAM scheduler. But there's an interrupt handler (JS_SetInterruptHandler) that checks a deadline on every JS opcode boundary — pass timeout: 1000 to eval and it interrupts after 1s, runtime stays usable. For contexts there's also max_reductions — QuickJS-NG counts JS operations and interrupts when the budget runs out, closest analog to BEAM reductions.

3. QuickJS-NG uses refcounting with cycle detection. Each runtime/context has its own GC — one collecting doesn't touch another. When a Runtime GenServer terminates, JS_FreeContext + JS_FreeRuntime release everything.

4. No, standard JS mutability. But the JS↔Erlang boundary copies values — no shared mutable state across that boundary.

5. QuickJS-NG enforces JS_SetMemoryLimit per-runtime (default 256 MB) and JS_SetContextMemoryLimit per-context. Exceeding the limit raises a JS exception, not a segfault. It propagates as {:error, ...} to the caller. Since each runtime is a supervised GenServer, the supervisor restarts it. There are tests for OOM in one context not crashing the pool, and one runtime crashing not affecting siblings.

— Memory limits: JS_SetMemoryLimit per-runtime (256 MB default), JS_SetContextMemoryLimit per-context. Exceeding → JS exception, not a crash.

— Execution limits: interrupt handler checks a nanosecond deadline every opcode. For contexts, max_reductions caps JS operations independently of wall-clock time.

— API surface: apis: false gives bare QuickJS — no fetch, no fs, no DOM, no I/O. You control exactly which Elixir functions JS can call via the handlers map. JS cannot call arbitrary Elixir code.

— Conversion limits: max_convert_depth (32) and max_convert_nodes (10k) prevent pathological objects from blowing up during JS↔BEAM conversion.

— Process isolation: separate OS thread, separate QuickJS heap per runtime.

No seccomp — QuickJS runs in-process so seccomp would restrict the entire BEAM. The sandbox boundary is QuickJS-NG's memory-safe interpreter (no JIT, no raw pointer access from JS) plus the API surface control above.