# Node.js APIs 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. > **Note** > > 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 import { AsyncLocalStorage } from "node:async_hooks"; import 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](/en/documentation/devtools/cli/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](https://github.com/aziontech/lib/blob/main/packages/unenv-preset/src/index.ts), 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!`. | Module | Status | Notes | | -------------------------------------------------------------------------- | ---------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | \_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 supported | `assert.strictEqual(1, 2)` throws an `AssertionError`. | | assert/strict | 🟡 Partially supported | — | | [async\_hooks](/en/documentation/devtools/runtime/node/async-hooks/) | 🟡 Partially supported | Only [AsyncLocalStorage](https://nodejs.org/api/async_context.html#class-asynclocalstorage) and [AsyncResource](https://nodejs.org/api/async_hooks.html#class-asyncresource) are implemented, and both work. [Code sample](https://github.com/aziontech/azion-samples/tree/dev/samples/node-async-hooks). | | [buffer](/en/documentation/devtools/runtime/node/buffer/) | 🟡 Partially supported | `Buffer` 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](/en/documentation/devtools/runtime/node/crypto/) | 🟡 Partially supported | `createHash()`, `createHmac()`, `randomBytes()`, `randomUUID()`, and `subtle` work. | | dgram | 🟢 Supported | — | | diagnostics\_channel | 🟢 Supported | — | | dns | 🔴 Build-only | `dns.lookup()` throws `Error: [unenv] dns.lookup is not implemented yet!`. | | dns/promises | 🔴 Build-only | — | | domain | 🟢 Supported | — | | [events](/en/documentation/devtools/runtime/node/events/) | 🟢 Supported | — | | [fs](/en/documentation/devtools/runtime/node/fs/) | 🟡 Partially supported | A 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 supported | On a path the build did not embed, `readFile()`, `writeFile()`, `readdir()`, and `stat()` reject with `Error: missing storage annotation`. | | [http](/en/documentation/devtools/runtime/node/http/) | 🟡 Partially supported | `http.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 supported | `https.get()` throws `Error: [unenv] https.get is not implemented yet!`. | | inspector | 🟢 Supported | — | | inspector/promises | 🟡 Partially supported | — | | [module](/en/documentation/devtools/runtime/node/module/) | 🟡 Partially supported | Behaves the same in a deployed function and under `azion dev`. `module.builtinModules` lists 65 names, and `module.createRequire()` returns `undefined`. | | net | 🟡 Partially supported | — | | [os](/en/documentation/devtools/runtime/node/os/) | 🟡 Partially supported | Every 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](/en/documentation/devtools/runtime/node/path/) | 🟢 Supported | Every function operates on path strings, without file system access. | | path/posix | 🟢 Supported | `path.posix.join()` returns the same paths as `path.join()`. | | path/win32 | 🟡 Partially supported | Joins segments with `/`: `path.win32.join("C:\\a", "b")` returns `C:/a/b`. | | perf\_hooks | 🟢 Supported | `performance.now()` is a function. | | [process](/en/documentation/devtools/runtime/node/process/) | 🟡 Partially supported | `process.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 supported | `querystring.stringify({ a: [1, 2], b: 'x y' })` returns `a=1&a=2&b=x%20y`. | | readline | 🟢 Supported | — | | readline/promises | 🟢 Supported | — | | repl | 🟡 Partially supported | — | | [stream](/en/documentation/devtools/runtime/node/stream/) | 🟡 Partially supported | `Readable`, `Writable`, `Duplex`, `Transform`, `PassThrough`, and the callback form of `pipeline()` work. | | stream/consumers | 🟡 Partially supported | — | | stream/promises | 🟡 Partially supported | `pipeline()` throws `Error: [unenv] stream.promises.pipeline is not implemented yet!`. | | stream/web | 🟢 Supported | — | | [string\_decoder](/en/documentation/devtools/runtime/node/string-decoder/) | 🟢 Supported | — | | sys | 🟡 Partially supported | — | | [timers](/en/documentation/devtools/runtime/node/timers/) | 🟡 Partially supported | A 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 supported | The async iterator that `setInterval()` returns yields one value and then ends. | | tls | 🟡 Partially supported | — | | trace\_events | 🟢 Supported | — | | tty | 🟢 Supported | — | | [url](/en/documentation/devtools/runtime/node/url/) | 🟡 Partially supported | `URL` and `URLSearchParams` are globals. `url.parse()`, `url.format()`, `url.resolve()`, `url.fileURLToPath()`, `url.pathToFileURL()`, and `url.domainToASCII()` work. | | [util](/en/documentation/devtools/runtime/node/utils/) | 🟡 Partially supported | `util.promisify()`, `util.inspect()`, and `util.format()` work. | | util/types | 🟡 Partially supported | `util.types.isNativeError()` throws `Error: [unenv] util.types.isNativeError is not implemented yet!`. | | v8 | 🟢 Supported | — | | [vm](/en/documentation/devtools/runtime/node/vm/) | 🟡 Partially supported | No method runs code: `runInThisContext()`, `runInNewContext()`, `runInContext()`, and `Script.runInThisContext()` throw `[unenv] … is not implemented yet!`. | | wasi | 🟢 Supported | — | | worker\_threads | 🟡 Partially supported | — | | [zlib](/en/documentation/devtools/runtime/node/zlib/) | 🟡 Partially supported | `zlib.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. | --- ## Related resources - [Web APIs](/en/documentation/devtools/runtime/api-reference/javascript.md): The Web APIs a function can call, such as fetch and the stream APIs. - [Frameworks compatibility](/en/documentation/devtools/runtime/frameworks/frameworks-compatibility.md): The web frameworks that build and run on Azion Runtime. - [Use Node.js APIs through polyfills](/en/documentation/guides/application-development/functions-and-runtime/use-polyfills.md): How the build resolves Node.js APIs through polyfills, shown in a JavaScript project. - [Globals](/en/documentation/devtools/runtime/api-reference/azion-runtime-globals.md): The global objects of Azion Runtime, which a function uses without an import.