# unenv preset The `@aziontech/unenv-preset` package is the [Azion Lib](/en/documentation/devtools/azion-lib/) preset for unenv: one configuration object that lists the Node.js globals, modules, and polyfills a build for [Azion Runtime](/en/documentation/devtools/runtime/) replaces. Azion Bundler, which the Azion CLI runs to build a project, applies the preset. The package has no functions to call: a [function](/en/documentation/platform/functions/) reaches the polyfills by importing `node:*` modules, such as `node:fs` and `node:crypto`. Install the package: ```bash npm install @aziontech/unenv-preset ``` The preset sample on this page is a JavaScript ES module that runs in Node.js. The function samples run inside a function served locally with [azion dev](/en/documentation/devtools/cli/dev-command/). For what `node:fs` returns in a deployed function, refer to [node:fs](/en/documentation/devtools/runtime/node/fs/). --- ## Preset object The default export of `@aziontech/unenv-preset` is the preset object, `{ inject, alias, external, polyfill }`. The package has no named exports, so `import { preset } from '@aziontech/unenv-preset'` returns `undefined`. Import the object as the default: ```javascript import preset from '@aziontech/unenv-preset'; // The package has a default export only: { inject, alias, external, polyfill } console.log('keys:', Object.keys(preset)); console.log('inject:', Object.keys(preset.inject)); console.log('alias:', Object.keys(preset.alias)); console.log('external:', preset.external); console.log('polyfill:', preset.polyfill); ``` Output: ```text keys: [ 'inject', 'alias', 'external', 'polyfill' ] inject: [ '__dirname', '__filename', 'import.meta.url', 'process', 'performance', 'setInterval', 'clearInterval', 'console', 'asyncStorage', 'dateToString' ] alias: [ '@aziontech/utils', '@aziontech/utils/edge', '@aziontech/utils/node', 'fetch-to-node', 'accepts', 'assert', 'buffer', 'https', 'module', 'string_decoder', 'timers', 'util', 'zlib' ] external: [ 'node:async_hooks', 'node:fs/promises', 'node:stream', 'node:crypto' ] polyfill: [ 'aziondev:async_hooks:/async-hooks/async-hooks.polyfills.js', 'aziondev:fs:/fs/fs.polyfills.js', 'aziondev:fs/promises:/fs/promises/promises.polyfills.js', 'aziondev:stream:/stream/stream.polyfills.js', 'aziondev:crypto:/crypto/crypto.polyfills.js', 'azionprd:fs:/fs.js' ] ``` The object has four properties: | Property | Type | Description | | ---------- | ---------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `inject` | `object` | The globals the build injects, each key mapped to a string. For the list, refer to [Global polyfills](#global-polyfills). | | `alias` | `object` | The module names the build maps to a replacement, each key mapped to a string: `@aziontech/utils`, `@aziontech/utils/edge`, `@aziontech/utils/node`, `fetch-to-node`, `accepts`, `assert`, `buffer`, `https`, `module`, `string_decoder`, `timers`, `util`, and `zlib`. | | `external` | `string[]` | Four module names: `node:async_hooks`, `node:fs/promises`, `node:stream`, and `node:crypto`. | | `polyfill` | `string[]` | The polyfill entries. Entries that start with `aziondev:` serve development builds and cover `async_hooks`, `fs`, `fs/promises`, `stream`, and `crypto`. The one `azionprd:` entry serves production builds and covers `fs`. | The build applies this object for you, so a project does not pass it to unenv by hand. The unenv preset is not the `preset` field of `build` in [azion.config.js](/en/documentation/devtools/cli/azion-config-js/#build), which names the framework or language preset of a project. --- ## Global polyfills The `inject` property of the unenv preset lists the Node.js globals that the build adds to a function. A function uses these globals as it would in Node.js, with nothing to import. | Global | Description | | ------------- | ----------------------------------------------------------------------------- | | `__dirname` | The name of the current directory. | | `__filename` | The name of the current file. | | `process` | Process information and the environment, including the environment variables. | | `performance` | Performance timing. | The preset also injects `import.meta.url`, `setInterval`, `clearInterval`, `console`, `asyncStorage`, and `dateToString`. --- ## Node.js modules in a function A function reaches the polyfills of the unenv preset through the Node.js module names. Import `node:fs` or `node:crypto` in the function code, and the build swaps in the polyfill when `build.polyfills` is `true` in [azion.config.js](/en/documentation/devtools/cli/azion-config-js/#build). The JavaScript template that `azion init` creates sets `polyfills` to `true`. Import the Node.js module, never a file of the package. The polyfill files of `@aziontech/unenv-preset` cannot be imported in Node.js or in a function, and the package has no `crypto` polyfill file. The messages each attempt returns are in [Errors](#errors). The `node:fs` calls read the files that `build.memoryFS` embeds in the build. A file is read by its path relative to `removePathPrefix`. The `node:fs` samples on this page use a project whose `azion.config.js` sets `build.memoryFS` to `{ injectionDirs: ['./data'], removePathPrefix: './data' }`. Its `data/` folder holds `hello.txt`, `index.html`, `about/index.html`, and `docs/readme.txt`, so `data/hello.txt` is read as `/hello.txt`. Under `azion dev`, `node:fs` reads the embedded files from the `.edge/storage/` folder of the project. The local `node:fs` has no `writeFileSync`, `mkdirSync`, or `readSync`. --- ## createHash and randomUUID The `createHash` and `randomUUID` functions come from `node:crypto`. `createHash` returns a hash object for an algorithm, such as `sha256`, and `randomUUID` returns a random UUID. For the full module, refer to [node:crypto](/en/documentation/devtools/runtime/node/crypto/). This function hashes a string and generates a UUID: ```javascript import { createHash, randomUUID } from 'node:crypto'; export default { async fetch() { // Create a hash const hash = createHash('sha256'); hash.update('some data'); const digest = hash.digest('hex'); // Generate a UUID const uuid = randomUUID(); return new Response(`sha256=${digest}\nuuid=${uuid}\n`); }, }; ``` Served locally with `azion dev`, the function returns: ```text $ curl http://localhost:3333/x HTTP/1.1 200 OK content-type: text/plain;charset=UTF-8 sha256=1307990e6ba5ca145eb35e99182a9bec46531bc54ddf656a602c780fa0240dee uuid=e2ebf3ce-e7e9-4393-855c-ccdd93ea26f3 ``` --- ## readFileSync The `readFileSync` function of `node:fs` reads the whole content of a file that `build.memoryFS` embeds in the build. | Parameter | Type | Required | Description | | --------- | -------- | -------- | -------------------------------------------------- | | `path` | `string` | Yes | The path of the file. | | `options` | — | No | Options for the read, such as the encoding `utf8`. | Returns the content of the file as a `string` or a `Buffer`. With the encoding `utf8`, the content is a `string`. This function returns the content of `/hello.txt`, the file `data/hello.txt` of the project: ```javascript import { readFileSync } from 'node:fs'; export default { async fetch() { // Read a file embedded with build.memoryFS (data/hello.txt is served as /hello.txt) const content = readFileSync('/hello.txt', 'utf8'); return new Response(content); }, }; ``` Served locally with `azion dev`, the function returns: ```text $ curl http://localhost:3333/x HTTP/1.1 200 OK content-type: text/plain;charset=UTF-8 Hello from memoryFS ``` --- ## readdirSync The `readdirSync` function of `node:fs` lists the content of a directory that `build.memoryFS` embeds in the build. | Parameter | Type | Required | Description | | --------- | -------- | -------- | -------------------------- | | `path` | `string` | Yes | The path of the directory. | | `options` | — | No | Options for the listing. | Returns a `string[]` with the names of the files and directories in the directory. This function lists the root directory and the `/docs` directory: ```javascript import { readdirSync } from 'node:fs'; export default { async fetch() { // List directory contents const files = readdirSync('/'); const docs = readdirSync('/docs'); return Response.json({ files, docs }); }, }; ``` Served locally with `azion dev`, the function returns: ```text $ curl http://localhost:3333/x HTTP/1.1 200 OK content-type: application/json {"files":["about","docs","hello.txt","index.html"],"docs":["readme.txt"]} ``` --- ## statSync and existsSync The `existsSync` function of `node:fs` checks whether a path exists in the files that `build.memoryFS` embeds. | Parameter | Type | Required | Description | | --------- | -------- | -------- | ------------------ | | `path` | `string` | Yes | The path to check. | Returns `true` when the path exists and `false` when it does not. The `statSync` function of `node:fs` returns the stats of a file or a directory. | Parameter | Type | Required | Description | | --------- | -------- | -------- | ---------------------------------- | | `path` | `string` | Yes | The path of the file or directory. | | `options` | — | No | Options for the call. | Returns an `fs.Stats` object, with `size`, `isFile()`, and `isDirectory()`. This function checks `/hello.txt`, reads its stats, and checks a path the build did not embed: ```javascript import { statSync, existsSync } from 'node:fs'; export default { async fetch() { const lines = []; // Check if file exists if (existsSync('/hello.txt')) { // Get file stats const stats = statSync('/hello.txt'); lines.push(`File size: ${stats.size}`); lines.push(`Is directory: ${stats.isDirectory()}`); lines.push(`Is file: ${stats.isFile()}`); } lines.push(`existsSync('/missing.txt'): ${existsSync('/missing.txt')}`); return new Response(lines.join('\n') + '\n'); }, }; ``` Served locally with `azion dev`, the function returns: ```text $ curl http://localhost:3333/x HTTP/1.1 200 OK content-type: text/plain;charset=UTF-8 File size: 20 Is directory: false Is file: true existsSync('/missing.txt'): false ``` --- ## openSync and closeSync The `openSync` function of `node:fs` opens a file. | Parameter | Type | Required | Description | | --------- | -------- | -------- | -------------------------------------- | | `path` | `string` | Yes | The path of the file. | | `flags` | `string` | Yes | The open mode, such as `'r'` or `'w'`. | | `mode` | — | No | The file mode. | Returns the file descriptor, a `number`. The `closeSync` function of `node:fs` closes a file descriptor. | Parameter | Type | Required | Description | | --------- | -------- | -------- | ----------------------------- | | `fd` | `number` | Yes | The file descriptor to close. | This function opens `/hello.txt` and closes its file descriptor: ```javascript import { openSync, closeSync } from 'node:fs'; export default { async fetch() { // Open file and get file descriptor const fd = openSync('/hello.txt', 'r'); // Close file descriptor closeSync(fd); return new Response(`opened and closed fd ${fd}\n`); }, }; ``` Served locally with `azion dev`, the function returns: ```text $ curl http://localhost:3333/x HTTP/1.1 200 OK content-type: text/plain;charset=UTF-8 opened and closed fd 17 ``` Under `azion dev`, the file descriptor is one the operating system assigns. --- ## Errors These messages appear when code imports a file of `@aziontech/unenv-preset` or calls a `node:fs` function the local runtime does not have. | Message | Cause | What to do | | -------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------- | | `ERR_MODULE_NOT_FOUND` `Cannot find module '…/node_modules/@aziontech/unenv-preset/src/polyfills/node/crypto'` | The code imports `@aziontech/unenv-preset/polyfills/node/crypto`. The package has no `crypto` polyfill file. | Import from `node:crypto` in a function, as in [createHash and randomUUID](#createhash-and-randomuuid). | | `TypeError: Cannot read properties of undefined (reading '__FILES__')` | A Node.js script imports `@aziontech/unenv-preset/polyfills/node/fs.js`. The file reads the embedded files of a build, which a Node.js script does not have. | Import from `node:fs` in a function that the Azion CLI builds. | | `ReferenceError: SRC_NODE_FS is not defined` | A function imports `@aziontech/unenv-preset/polyfills/node/fs.js`, and `azion dev` stops at server start. | Import from `node:fs`, as in [readFileSync](#readfilesync). | | `TypeError: (void 0) is not a function` | A function calls `writeFileSync`, `mkdirSync`, or `readSync` from `node:fs` under `azion dev`. The build warns that the import `will always be undefined because there is no matching export in "internal-env-dev:fs"`. | Read files with the calls on this page. | --- ## Related resources - [How Azion Lib works](/en/documentation/devtools/azion-lib/how-it-works.md): Where each Azion Lib module runs, in Node.js or in a function, and what differs between the two. - [Use Node.js APIs through polyfills](/en/documentation/guides/application-development/functions-and-runtime/use-polyfills.md): Create a function project, import a Node.js API, and run it locally and deployed. - [Node.js APIs](/en/documentation/devtools/runtime/node.md): The Node.js modules Azion Runtime resolves, with the behavior of each one. - [azion.config.js](/en/documentation/devtools/cli/azion-config-js.md): The `build.polyfills` and `build.memoryFS` settings that decide which polyfills and files a build carries.