# How can I use files in Vercel Functions? **Author:** Lee Robinson --- This guide will explain how to read files from Vercel Functions, both when used with frameworks like Next.js or standalone on Vercel. We’ll explain how bundling works, how you can tell Vercel to include additional files for use at runtime in your functions, and more. ## How bundling application code works Your application gets bundled during a build to include all necessary user code and dependencies needed for runtime. Both Next.js and general Vercel Functions use Vercel’s [Node File Trace](https://github.com/vercel/nft) to determine which files (including those in `node_modules`) are necessary to be included. This uses static analysis to inspect any `import`, `require`, and `fs` usage and determine all files that a page might load. ## Examples of reading files ### Using `process.cwd()` We recommend using `process.cwd()` to determine the current directory of the Vercel Function instead of using `__dirname`. For example, this function reads the file `users.json` from the root of the repository. `import fs from 'fs'; import path from 'path'; export function GET(request) { let usersPath = path.join(process.cwd(), 'users.json'); let file = fs.readFileSync(usersPath); return new Response(file); }` ### Using dynamic `require` If you are trying to write your code using ES Modules, sometimes you might rely on CommonJS code. To dynamically require and include a function using CJS, you can write a function as follows: `import { createRequire } from 'node:module'; let sayHello = createRequire(import.meta.url)('../greet.cjs'); export function GET(request) { return new Response(sayHello()); }` This function `api/file.js` is requiring `greet.cjs`, which is in the root of the repository. `function sayHello() { return 'Hello, World!'; } module.exports = sayHello;` To test this locally, ensure your `package.json` is configured for ES Modules: `{ "type": "module" }` Finally, to tell Vercel to include the `greet.cjs` file while bundling, modify `vercel.json`: `{ "functions": { "api/file.js": { "includeFiles": "greet.cjs" } } }` ### Using Next.js Since Next.js has its own build process which uses Node File Trace, you would use the [built-in functionality](https://nextjs.org/docs/pages/api-reference/next-config-js/output#caveats) of the framework to include additional files rather than `vercel.json`. The file path can be a [glob](https://www.npmjs.com/package/minimatch) to select multiple files. Notably, if you are trying to read files from `node_modules`, you will need to add this to `outputFileTracingIncludes`. `module.exports = { experimental: { outputFileTracingIncludes: { '/api/another': ['./necessary-folder/**/*'], }, }, }` Further, sometimes if you are using a [monorepo](https://vercel.com/docs/monorepos), you’ll have a different root directory for your application. To include files outside of that folder with Next.js, you can use: `module.exports = { experimental: { // includes files from the monorepo base two directories up outputFileTracingRoot: path.join(__dirname, '../../'), }, }` ### Using SvelteKit SvelteKit uses Node File Trace and also supports the ability to read files. You do not need to modify `vercel.json` with this approach. `import { read } from '$app/server'; import users from './users.json'; export async function load() { return { users: await read(users).text() }; }` ### Using Astro Astro uses Node File Trace and also supports the ability to [include](https://docs.astro.build/en/guides/integrations-guide/vercel/#includefiles) or [exclude](https://docs.astro.build/en/guides/integrations-guide/vercel/#excludefiles) files. You do not need to modify `vercel.json` with this approach. `import { defineConfig } from 'astro/config'; import vercel from '@astrojs/vercel/serverless'; export default defineConfig({ output: 'server', adapter: vercel({ includeFiles: ['./users.json'], }), });` ### Using Nuxt Nuxt can use [server assets](https://github.com/pi0/nuxt-server-assets) to include files into your Vercel Function. Any file inside `server/assets/` is by default included. You can access server assets using [storage](https://nitro.unjs.io/guide/storage) API. `export default defineEventHandler(async () => { // https://nitro.unjs.io/guide/assets#server-assets const assets = useStorage('assets:server') const users = await assets.getItem('users.json') return { users } })` ## Examples of writing files If you are looking for a way to write files, we recommend persisting to object storage like [Vercel Blob](https://vercel.com/docs/storage/vercel-blob) or similar solutions. --- [View full KB sitemap](/kb/sitemap.md)