Node.js APIs

The Node.js modules a function can import in Azion Runtime, the support status of each one, and what their calls return or throw.

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Azion Runtime is compatible with a part of the Node.js APIs, not with all of them. A function, and every npm package it depends on, can import the 68 Node.js modules in the table below. Each one resolves when the build bundles the function, and loads in a deployed function and under azion dev. The status of a module says how much of its API works when the function calls it.

Under azion dev, some modules behave differently from a deployed function. node:fs paths resolve under the .edge/storage/ folder of the project, an import of pipeline from node:stream fails the build, and timingSafeEqual() and generateKeyPairSync() from node:crypto throw.

Module imports

A function imports a Node.js module with the standard import syntax and the node: prefix:

JavaScript
01import { AsyncLocalStorage } from "node:async_hooks";
02import os from "node:os";

A polyfill is code that adds a feature to an environment that lacks it. The build resolves through polyfills the Node.js APIs that the runtime does not provide, and the polyfills setting of azion.config.js sets whether the build adds them. The list of APIs the build resolves through polyfills is in the @aziontech/unenv-preset package, which also accepts contributions.

Module support

The table lists each module with its status. Where a module page exists, the module name links to it. The Notes column states what a function receives when it calls the module, where that behavior is known.

  • 🟢 Supported: the API works normally at runtime.
  • 🟡 Partially supported: only some methods or features are available.
  • 🔴 Build-only: the module is included so the build completes without errors, but its API calls do not work at runtime.

About the Azion Cells runtime environment — A function on Azion runs inside a Cell, the isolation environment Azion builds on V8 isolates. A Cell is a lightweight, secure execution context, and the code inside it has no direct access to the operating system underneath.

For multi-tenant security and infrastructure integrity, a Cell does not give a function:

  • The properties of the machine that runs it. node:os and process return fixed values instead, such as linux for os.platform(), an empty string for os.hostname(), and 0 for os.totalmem().
  • DNS resolution through native system calls (node:dns, node:dns/promises).
  • Low-level TCP or UDP sockets that require direct system calls.

The modules marked 🔴 Build-only are included as stubs, so that npm packages with static imports of them still build. Their calls do not work at runtime: dns.lookup() throws Error: [unenv] dns.lookup is not implemented yet!.

ModuleStatusNotes
_http_agent🟡 Partially supported—
_http_client🟡 Partially supported—
_http_common🟡 Partially supported—
_http_incoming🟡 Partially supported—
_http_outgoing🟡 Partially supported—
_http_server🟡 Partially supported—
_stream_duplex🟡 Partially supported—
_stream_passthrough🟡 Partially supported—
_stream_readable🟡 Partially supported—
_stream_transform🟡 Partially supported—
_stream_wrap🟡 Partially supported—
_stream_writable🟡 Partially supported—
_tls_common🟡 Partially supported—
_tls_wrap🟡 Partially supported—
assert🟡 Partially supportedassert.strictEqual(1, 2) throws an AssertionError.
assert/strict🟡 Partially supported—
async_hooks🟡 Partially supportedOnly AsyncLocalStorage and AsyncResource are implemented, and both work. Code sample.
buffer🟡 Partially supportedBuffer is also a global. The module-level functions, such as buffer.isAscii(), are not supported.
child_process🟡 Partially supported—
cluster🟢 Supported—
console🟢 Supported—
constants🟢 Supported—
crypto🟡 Partially supportedcreateHash(), createHmac(), randomBytes(), randomUUID(), and subtle work.
dgram🟢 Supported—
diagnostics_channel🟢 Supported—
dns🔴 Build-onlydns.lookup() throws Error: [unenv] dns.lookup is not implemented yet!.
dns/promises🔴 Build-only—
domain🟢 Supported—
events🟢 Supported—
fs🟡 Partially supportedA function cannot write files: fs.writeFileSync() throws Error: unsupported. Synchronous reads use the in-memory file system that the build.memoryFS setting fills. On a path the build did not embed, fs.readFileSync() throws ENOENT, and the callback fs.readFile() receives Error: missing storage annotation.
fs/promises🟡 Partially supportedOn a path the build did not embed, readFile(), writeFile(), readdir(), and stat() reject with Error: missing storage annotation.
http🟡 Partially supportedhttp.STATUS_CODES and http.METHODS are readable. http.request(), http.get(), and http.createServer() throw [unenv] … is not implemented yet!.
http2🟡 Partially supported—
https🟡 Partially supportedhttps.get() throws Error: [unenv] https.get is not implemented yet!.
inspector🟢 Supported—
inspector/promises🟡 Partially supported—
module🟡 Partially supportedBehaves the same in a deployed function and under azion dev. module.builtinModules lists 65 names, and module.createRequire() returns undefined.
net🟡 Partially supported—
os🟡 Partially supportedEvery member returns without throwing, with fixed values that do not describe the machine: os.platform() returns linux, os.type() returns Linux, and os.hostname() returns an empty string.
path🟢 SupportedEvery function operates on path strings, without file system access.
path/posix🟢 Supportedpath.posix.join() returns the same paths as path.join().
path/win32🟡 Partially supportedJoins segments with /: path.win32.join("C:\\a", "b") returns C:/a/b.
perf_hooks🟢 Supportedperformance.now() is a function.
process🟡 Partially supportedprocess.env holds the environment variables of your account: read one as process.env.VAR_NAME. process.platform and process.arch are empty strings, and process.pid is 200.
punycode🟡 Partially supported—
querystring🟡 Partially supportedquerystring.stringify({ a: [1, 2], b: 'x y' }) returns a=1&a=2&b=x%20y.
readline🟢 Supported—
readline/promises🟢 Supported—
repl🟡 Partially supported—
stream🟡 Partially supportedReadable, Writable, Duplex, Transform, PassThrough, and the callback form of pipeline() work.
stream/consumers🟡 Partially supported—
stream/promises🟡 Partially supportedpipeline() throws Error: [unenv] stream.promises.pipeline is not implemented yet!.
stream/web🟢 Supported—
string_decoder🟢 Supported—
sys🟡 Partially supported—
timers🟡 Partially supportedA timer callback must be a function: a string or a number in its place throws EvalError: eval not allowed on setTimeout/setInterval parameter.
timers/promises🟡 Partially supportedThe async iterator that setInterval() returns yields one value and then ends.
tls🟡 Partially supported—
trace_events🟢 Supported—
tty🟢 Supported—
url🟡 Partially supportedURL and URLSearchParams are globals. url.parse(), url.format(), url.resolve(), url.fileURLToPath(), url.pathToFileURL(), and url.domainToASCII() work.
util🟡 Partially supportedutil.promisify(), util.inspect(), and util.format() work.
util/types🟡 Partially supportedutil.types.isNativeError() throws Error: [unenv] util.types.isNativeError is not implemented yet!.
v8🟢 Supported—
vm🟡 Partially supportedNo method runs code: runInThisContext(), runInNewContext(), runInContext(), and Script.runInThisContext() throw [unenv] … is not implemented yet!.
wasi🟢 Supported—
worker_threads🟡 Partially supported—
zlib🟡 Partially supportedzlib.constants is available, but no function compresses data: zlib.gzipSync() throws Error: [unenv] zlib.gzipSync is not implemented yet!. To compress data, use the Web CompressionStream API.
Web APIs

The Web APIs a function can call, such as fetch and the stream APIs.

Frameworks compatibility

The web frameworks that build and run on Azion Runtime.

Use Node.js APIs through polyfills

How the build resolves Node.js APIs through polyfills, shown in a JavaScript project.

Globals

The global objects of Azion Runtime, which a function uses without an import.