Next.js provides two server runtimes:
- Node.js Runtime (default): full Node.js API surface, used for rendering and route handlers.
- Edge Runtime: a subset of Web APIs, optimized for low-latency responses at the edge. Used in Middleware.
Choosing a runtime
| Node.js | Edge |
|---|
| Cold start | Slower | Faster |
| Node.js APIs | Full | None |
node_modules | All | ES Modules only (no native addons) |
| Streaming | Yes | Yes |
| ISR | Yes | No |
Setting the runtime
Specify the runtime in a Route Handler or layout/page segment using the runtime export:
export const runtime = 'edge'
'edge' or 'nodejs'. When omitted, the Node.js runtime is used.
ISR (Incremental Static Regeneration) is not supported in the Edge Runtime.
Supported APIs
Network APIs
| API | Description |
|---|
Blob | Represents a blob |
fetch | Fetches a resource |
FetchEvent | Represents a fetch event |
File | Represents a file |
FormData | Represents form data |
Headers | Represents HTTP headers |
Request | Represents an HTTP request |
Response | Represents an HTTP response |
URLSearchParams | Represents URL search parameters |
WebSocket | Represents a WebSocket connection |
Encoding APIs
| API | Description |
|---|
atob | Decodes a base-64 encoded string |
btoa | Encodes a string in base-64 |
TextDecoder | Decodes a Uint8Array into a string |
TextDecoderStream | Chainable decoder for streams |
TextEncoder | Encodes a string into a Uint8Array |
TextEncoderStream | Chainable encoder for streams |
Stream APIs
| API | Description |
|---|
ReadableStream | Represents a readable stream |
ReadableStreamBYOBReader | Reader for a ReadableStream |
ReadableStreamDefaultReader | Default reader for a ReadableStream |
TransformStream | Represents a transform stream |
WritableStream | Represents a writable stream |
WritableStreamDefaultWriter | Writer for a WritableStream |
Crypto APIs
| API | Description |
|---|
crypto | Access to platform cryptographic functions |
CryptoKey | Represents a cryptographic key |
SubtleCrypto | Low-level cryptographic primitives (hashing, signing, encryption) |
Web Standard APIs
All standard JavaScript globals are available: Array, ArrayBuffer, Boolean, Date, Error, JSON, Map, Math, Number, Object, Promise, Proxy, RegExp, Set, String, Symbol, URL, URLPattern, URLSearchParams, WeakMap, WeakSet, WebAssembly, timer functions (clearInterval, clearTimeout, setInterval, setTimeout), encoding helpers (decodeURI, decodeURIComponent, encodeURI, encodeURIComponent), typed arrays, AbortController, console, DOMException, queueMicrotask, structuredClone, and more.
Next.js polyfills
AsyncLocalStorage (Node.js async_hooks API)
Environment variables
const value = process.env.MY_VAR
process.env is available in both next dev and next build.
Unsupported APIs
The following are not available in the Edge Runtime:
- Native Node.js APIs (filesystem,
crypto module, Buffer, etc.)
- CommonJS
require() — use ES module import instead
node_modules packages that use native Node.js APIs
The following JavaScript features are also disabled:
| API | Description |
|---|
eval | Evaluates a JavaScript string as code |
new Function(code) | Creates a function from a string |
WebAssembly.compile | Compiles a WASM module from a buffer |
WebAssembly.instantiate | Compiles and instantiates a WASM module from a buffer |
Allowing dynamic code evaluation
In rare cases where code contains unreachable dynamic evaluation, you can suppress the build error using unstable_allowDynamic in your Proxy config:
export const config = {
unstable_allowDynamic: [
'/lib/utilities.js',
'**/node_modules/function-bind/**',
],
}
If the allowed statements are executed at runtime on the Edge, they will throw a runtime error. Use unstable_allowDynamic only for code paths that are guaranteed not to execute.
Version history
| Version | Changes |
|---|
v12.0.0 | Edge Runtime introduced |
