Expo Server

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Server-side API and runtime for Expo Router projects.

Server

expo-server is a server-side API and runtime library for Expo Router. It provides helpers you can use in your Expo Router API routes or other server code, and contains adapters to run Expo Router server exports.

Installation

Terminal

- npx expo install expo-server

To use expo-server in your project, you need to configure your Expo Router project to export in server mode. Follow the instructions from Expo Router's API Routes guide:

API Routes

Learn how to create server endpoints with Expo Router.

Usage

expo-server's runtime APIs can only be used in server-side code and give you access to the server-side runtime environment. The runtime API exposes functions that can be called within the async context of request handlers and give you information about the current request or schedule tasks that run concurrently to the incoming request.

Accessing request metadata

import { origin, environment } from 'expo-server';

export async function GET() {
  return Response.json({
    isProduction: environment() == null,
    isStating: environment() === 'staging',
    origin: origin(),
  });
}

Scheduling tasks

import { runTask, deferTask } from 'expo-server';

export async function GET() {
  runTask(async () => {
    console.log('will run immediately.');
  });

  deferTask(async () => {
    console.log('will run after the response resolved.');
  });

  return Response.json({ success: true });
}

Adapters

expo-server exposes adapters to run Expo Router server-side exports in different environments or on different cloud provider serverless functions. Typically, every runtime needs its own adapter to function with the expo-server runtime. Before deploying to these providers, it is good to be familiar with the basics of npx expo export command.

Adapter	Provider
`expo-server/adapter/bun`	Bun
`expo-server/adapter/express`	Express
`expo-server/adapter/http`	Node.js
`expo-server/adapter/netlify`	Netlify Functions
`expo-server/adapter/vercel`	Vercel Functions
`expo-server/adapter/workerd`	Cloudflare Workers

To learn how to host API routes on different third-party services, follow the instructions from Expo Router's API Routes guide:

API Routes

Learn how to host API Routes on third-party services.

By convention, all adapters export a createRequestHandler function that accepts a parameters object. This accepts a build parameter that must be set to the relative path to the dist/server output directory that npx expo export created. Some adapters may also accept more values to configure the runtime API.

import path from 'node:path';
import { createRequestHandler } from 'expo-server/adapter/http';

const onRequest = createRequestHandler({
  build: path.join(process.cwd(), 'dist/server'),
  environment: process.env.NODE_ENV,
});

API

Classes

`StatusError`

Server

Type: Class extends Error

An error response representation which can be thrown anywhere in server-side code.

A StatusError can be thrown by a request handler and will be caught by the expo-server runtime and replaced by a Response with the status and body that's been passed to the StatusError.

Example

import { StatusError } from 'expo-server';

export function GET(request, { postId }) {
  if (!postId) {
    throw new StatusError(400, 'postId parameter is required');
  }
}

StatusError Properties

`body`

Server

Type: string

`status`

Server

Type: number

Methods

`deferTask(fn)`

Server

Parameter	Type	Description
fn	`() => void \| Promise<unknown>`	A task function to execute after the request handler has finished.

Defers a task until after a response has been sent.

This only calls the task function once the request handler has finished resolving a Response and keeps the request handler alive until the task is completed. This is useful to run non-critical tasks after the request handler, for example to log analytics datapoints. If the request handler rejects with an error, deferred tasks won't be executed.

Returns:

void

`environment()`

Server

Returns the request's environment, if the server runtime supports this.

In EAS Hosting, the returned environment name is the alias or deployment identifier, but the value may differ for other providers.

Returns:

string | null

A request environment name, or null for production.

`origin()`

Server

Returns the current request's origin URL.

This typically returns the request's Origin header, which contains the request origin URL or defaults to null.

Returns:

string | null

A request origin

`runTask(fn)`

Server

Parameter	Type	Description
fn	`() => Promise<unknown>`	A task function to execute. The request handler will be kept alive until this task finishes.

Runs a task immediately and instructs the runtime to complete the task.

A request handler may be terminated as soon as the client has finished the full Response and unhandled promise rejections may not be logged properly. To run tasks concurrently to a request handler and keep the request alive until the task is completed, pass a task function to runTask instead. The request handler will be kept alive until the task completes.

Returns:

void

`setResponseHeaders(updateHeaders)`

Server

Parameter	Type	Description
updateHeaders	`Headers \| Record<string, string \| string[]> \| (headers: Headers) => void \| Headers`	A `Headers` object, a record of headers, or a function that receives `Headers` to be updated or can return a `Headers` object that will be merged into the response headers.

Sets headers on the Response the current request handler will return.

This only updates the headers once the request handler has finished and resolved a Response. It will either receive a set of Headers or an equivalent object containing headers, which will be merged into the response's headers once it's returned.

Returns:

void

Interfaces

`ImmutableRequest`

Server

Extends: _ImmutableRequest

An immutable version of the Fetch API's Request as received by middleware functions. It cannot be mutated or modified, its headers are immutable, and you won't have access to the request body.

Property	Type	Description
method	`string`	The `method` read-only property of the `POST`, etc.) A String indicating the method of the request. MDN Reference
url	`string`	The `url` read-only property of the Request interface contains the URL of the request. MDN Reference

`MiddlewareMatcher`

Server

Middleware matcher settings that restricts the middleware to run conditionally.

Property	Type	Description
methods(optional)	`string[]`	Set this to a list of HTTP methods to conditionally run middleware on. By default, middleware will match all HTTP methods. Example `['POST', 'PUT', 'DELETE']`
patterns(optional)	`(string \| RegExp)[]`	Set this to a list of path patterns to conditionally run middleware on. This may be exact paths, paths containing parameter or catch-all segments (`'/posts/[postId]'` or `'/blog/[...slug]'`), or regular expressions matching paths. Example `['/api', '/posts/[id]', '/blog/[...slug]']`

`MiddlewareSettings`

Server

Exported from a +middleware.ts file to configure the server-side middleware function.

See: https://docs.expo.dev/router/reference/middleware/

Example

import type { MiddlewareSettings } from 'expo-server';

export const unstable_settings: MiddlewareSettings = {
  matcher: {
    methods: ['GET'],
    patterns: ['/api', '/admin/[...path]'],
  },
};

Property	Type	Description
matcher(optional)	`MiddlewareMatcher`	Matcher definition that restricts the middleware to run conditionally.

Types

`MiddlewareFunction(request)`

Server

Middleware function type. Middleware run for every request in your app, or on specified conditonally matched methods and path patterns, as per MiddlewareMatcher.

See: https://docs.expo.dev/router/reference/middleware/

Example

import type { MiddlewareFunction } from 'expo-server';

const middleware: MiddlewareFunction = async (request) => {
  console.log(`Middleware executed for: ${request.url}`);
};

export default middleware;

Parameter	Type	Description
request	`ImmutableRequest`	An `ImmutableRequest` with read-only headers and no body access

Returns:

Promise<Response | void> | Response | void