Edge Runtime

The Next.js Edge Runtime is used for Middleware and supports the following 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	Represents a reader of a ReadableStream
ReadableStreamDefaultReader	Represents a reader of a ReadableStream
TransformStream	Represents a transform stream
WritableStream	Represents a writable stream
WritableStreamDefaultWriter	Represents a writer of a WritableStream

Crypto APIs

API	Description
crypto	Provides access to the cryptographic functionality of the platform
CryptoKey	Represents a cryptographic key
SubtleCrypto	Provides access to common cryptographic primitives, like hashing, signing, encryption or decryption

Web Standard APIs

API	Description
AbortController	Allows you to abort one or more DOM requests as and when desired
Array	Represents an array of values
ArrayBuffer	Represents a generic, fixed-length raw binary data buffer
Atomics	Provides atomic operations as static methods
BigInt	Represents a whole number with arbitrary precision
BigInt64Array	Represents a typed array of 64-bit signed integers
BigUint64Array	Represents a typed array of 64-bit unsigned integers
Boolean	Represents a logical entity and can have two values: true and false
clearInterval	Cancels a timed, repeating action which was previously established by a call to setInterval()
clearTimeout	Cancels a timed, repeating action which was previously established by a call to setTimeout()
console	Provides access to the browser's debugging console
DataView	Represents a generic view of an ArrayBuffer
Date	Represents a single moment in time in a platform-independent format
decodeURI	Decodes a Uniform Resource Identifier (URI) previously created by encodeURI or by a similar routine
decodeURIComponent	Decodes a Uniform Resource Identifier (URI) component previously created by encodeURIComponent or by a similar routine
DOMException	Represents an error that occurs in the DOM
encodeURI	Encodes a Uniform Resource Identifier (URI) by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the character
encodeURIComponent	Encodes a Uniform Resource Identifier (URI) component by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the character
Error	Represents an error when trying to execute a statement or accessing a property
EvalError	Represents an error that occurs regarding the global function eval()
Float32Array	Represents a typed array of 32-bit floating point numbers
Float64Array	Represents a typed array of 64-bit floating point numbers
Function	Represents a function
Infinity	Represents the mathematical Infinity value
Int8Array	Represents a typed array of 8-bit signed integers
Int16Array	Represents a typed array of 16-bit signed integers
Int32Array	Represents a typed array of 32-bit signed integers
Intl	Provides access to internationalization and localization functionality
isFinite	Determines whether a value is a finite number
isNaN	Determines whether a value is NaN or not
JSON	Provides functionality to convert JavaScript values to and from the JSON format
Map	Represents a collection of values, where each value may occur only once
Math	Provides access to mathematical functions and constants
Number	Represents a numeric value
Object	Represents the object that is the base of all JavaScript objects
parseFloat	Parses a string argument and returns a floating point number
parseInt	Parses a string argument and returns an integer of the specified radix
Promise	Represents the eventual completion (or failure) of an asynchronous operation, and its resulting value
Proxy	Represents an object that is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc)
queueMicrotask	Queues a microtask to be executed
RangeError	Represents an error when a value is not in the set or range of allowed values
ReferenceError	Represents an error when a non-existent variable is referenced
Reflect	Provides methods for interceptable JavaScript operations
RegExp	Represents a regular expression, allowing you to match combinations of characters
Set	Represents a collection of values, where each value may occur only once
setInterval	Repeatedly calls a function, with a fixed time delay between each call
setTimeout	Calls a function or evaluates an expression after a specified number of milliseconds
SharedArrayBuffer	Represents a generic, fixed-length raw binary data buffer
String	Represents a sequence of characters
structuredClone	Creates a deep copy of a value
Symbol	Represents a unique and immutable data type that is used as the key of an object property
SyntaxError	Represents an error when trying to interpret syntactically invalid code
TypeError	Represents an error when a value is not of the expected type
Uint8Array	Represents a typed array of 8-bit unsigned integers
Uint8ClampedArray	Represents a typed array of 8-bit unsigned integers clamped to 0-255
Uint32Array	Represents a typed array of 32-bit unsigned integers
URIError	Represents an error when a global URI handling function was used in a wrong way
URL	Represents an object providing static methods used for creating object URLs
URLPattern	Represents a URL pattern
URLSearchParams	Represents a collection of key/value pairs
WeakMap	Represents a collection of key/value pairs in which the keys are weakly referenced
WeakSet	Represents a collection of objects in which each object may occur only once
WebAssembly	Provides access to WebAssembly

Next.js Specific Polyfills

• AsyncLocalStorage

Environment Variables

You can use process.env to access Environment Variables for both next dev and next build.

Unsupported APIs

The Edge Runtime has some restrictions including:

• Native Node.js APIs are not supported. For example, you can't read or write to the filesystem.
• node_modules can be used, as long as they implement ES Modules and do not use native Node.js APIs.
• Calling require directly is not allowed. Use ES Modules instead.

The following JavaScript language features are disabled, and will not work:

API	Description
eval	Evaluates JavaScript code represented as a string
new Function(evalString)	Creates a new function with the code provided as an argument
WebAssembly.compile	Compiles a WebAssembly module from a buffer source
WebAssembly.instantiate	Compiles and instantiates a WebAssembly module from a buffer source

In rare cases, your code could contain (or import) some dynamic code evaluation statements which can not be reached at runtime and which can not be removed by treeshaking. You can relax the check to allow specific files with your Middleware configuration:

export const config = {
  unstable_allowDynamic: [
    // allows a single file
    '/lib/utilities.js',
    // use a glob to allow anything in the function-bind 3rd party module
    '/node_modules/function-bind/**',
  ],
}

unstable_allowDynamic is a glob, or an array of globs, ignoring dynamic code evaluation for specific files. The globs are relative to your application root folder.

Be warned that if these statements are executed on the Edge, they will throw and cause a runtime error.