JavaScript Runtime

The JavaScript runtime is powered by the Rivet Secure Exec project, which provides the isolated V8 runtime that agentOS runs guest code in. Every guest VM executes its JavaScript inside this runtime, fully sandboxed from the host.

JavaScript Acceleration

• JavaScript is unusually slow as WebAssembly: unlike most software, JavaScript pays a heavy penalty when compiled to WebAssembly, because so much engineering has gone into JIT-compiling JavaScript directly in V8.
• Native V8, full JIT: agentOS therefore runs guest JavaScript on the native V8 engine with its full JIT compiler, not through a WASM translation layer. We call this JavaScript Acceleration.
• Native-speed execution: guest JavaScript runs at native speed while staying inside the isolation boundary, with normal Node.js semantics.

Comparison to Node.js efficiency

• Isolate model, not processes: agentOS runs each agent inside a V8 isolate rather than spawning a full Node.js process per agent.
• Low memory overhead: an isolate carries far less per-agent memory overhead than a full Node.js process, so many agents fit in the footprint that a process-per-agent model would spend on a handful.
• Benchmarks: see the Secure Exec benchmarks for cold start, warm execution, and reuse measurements.

Node.js compatibility

Guest code runs as Node.js (reporting process.version as v22.0.0), but it never touches the host runtime. Every node: builtin resolves to a kernel-backed bridge or an in-isolate polyfill, never the real host module. For the full builtin matrix (fs, net, http, crypto, undici-backed fetch, and more), see the Secure Exec Node.js Compatibility reference.

npm packages

By default the VM has no npm packages installed. Mount a host node_modules directory to give guest code access to real packages: the nodeModulesMount helper projects it read-only at /root/node_modules, and the in-kernel resolver walks it exactly like Node.js does, with no bundling or patching.

import { agentOS, setup, nodeModulesMount } from "@rivet-dev/agentos";

const vm = agentOS({
  // Project a host node_modules tree into the VM (read-only by default).
  mounts: [nodeModulesMount("/absolute/path/to/node_modules")],
});

export const registry = setup({ use: { vm } });
registry.start();

Resolution matches naive Node.js over the mounted tree: the ancestor node_modules walk, package.json exports/imports and conditions, and realpath/symlink following (so pnpm and yarn layouts resolve too). Both ESM import and CommonJS require work. See the Secure Exec module loading guide for the full model.