node-compat modules

require("node:*") (and the bare aliases) resolve to Lifo's own implementations, written against the kernel. They aren't the real Node modules and they aren't WASM — they're TypeScript that reproduces the observable behavior real packages depend on.

What's implemented#

• Filesystem — fs and fs/promises over the VFS: readFile/writeFile, readdir (with withFileTypes), stat/lstat, mkdir, rm/rmdir, open flags, createReadStream/createWriteStream, and watch/watchFile (returning a real StatWatcher) wired to VFS watch events.
• Networking — http/https (servers that register on the port registry, and a client that goes through the proxying fetch), plus net/tls sockets and a dns resolver. dgram is a no-op shim (enough for tools that probe mDNS).
• Process & OS — process (argv, env, cwd, exit, stdio, hrtime, nextTick), os (platform() returns "lifo", cpus() returns 1 so worker-forking tools run in-band), child_process (exec/execFile/spawn bridged to real VM commands via executeCapture).
• Streams & encoding — stream (Readable/Writable/Transform, finished, pipeline, web-stream interop), stream/promises, string_decoder, buffer (a Buffer whose subarray/slice share memory like Node's), zlib.
• Crypto — hashing (md5, sha family), randomBytes, and digest encodings including base64url (which ubiquitous tools like write-file-atomic depend on for temp filenames).
• Runtime plumbing — events (a function-constructor EventEmitter, so EventEmitter.call(this) works), util (+types, debuglog), readline (with real keypress parsing), tty, timers (returning Timeout objects with ref/unref/refresh), module (a constructable Module class), async_hooks, diagnostics_channel, console, assert, url, path.

Why the small behaviors matter#

Most of the effort in the compat layer is in the details that a real package trips over. A few representative examples:

• Buffer#subarray must share memory (like Node), or msgpackr's encodeInto writes into a throwaway buffer and Metro's transform cache decodes garbage.
• crypto digests must support base64url, or atomic file writes name their temp file with binary garbage and every write ENOENTs.
• child_process stdout must emit close after end, or Metro's file crawler waits forever and the first bundle hangs.
• os.cpus() returning 1 makes jest-worker/Metro run in-band, avoiding a fake child_process fork that would hang.

These aren't hacks so much as the actual contract of the Node API. Getting them right is what lets create-expo-app, Vite, and Metro run unmodified.

Networking specifics#

Because a browser tab can't make arbitrary cross-origin requests, the compat layer routes outbound HTTP through a CORS proxy for known non-CORS hosts (e.g. api.expo.dev). This is injected as the fetch a module receives, and require("fetch-nodeshim") is served from the same stack, so a package's networking is transparently proxied without overriding globalThis.fetch. See Networking and Tunnelling.