Edge Runtime

Learn about the Edge runtime, the environment in which Edge Functions run.
Table of Contents

Functions using the Edge Runtime, are ideal for a cost-effective option that use a limited set of Web Standard APIs that make sense on the server. The Edge runtime is built on top of the V8 engine, allowing it to run in isolated execution environments that don't require a container or virtual machine.

Functions using the Edge runtime execute in the data center is closest to the user, or in a region near your databases. This can result in a much lower latency and allows you to provide personalization at speed.

Edge Functions run after the cache and so are ideal to be used on specific, dynamic parts of your site once the page is loaded. This response can be cached on the Edge Network making future invocations even faster.

See the quickstart to learn how to create your first function with the Edge runtime.

The Edge runtime provides a subset of Web APIs such as fetch, Request, and Response. This lightweight API layer is built to be performant and execute code with minimal latency.

The following tables list the APIs that are available in the Edge runtime.

APIDescription
fetchFetches a resource
RequestRepresents an HTTP request
ResponseRepresents an HTTP response
HeadersRepresents HTTP headers
FormDataRepresents form data
FileRepresents a file
BlobRepresents a blob
URLSearchParamsRepresents URL search parameters
BlobRepresents a blob
EventRepresents an event
EventTargetRepresents an object that can handle events
PromiseRejectEventRepresents an event that is sent to the global scope of a script when a JavaScript Promise is rejected
APIDescription
TextEncoderEncodes a string into a Uint8Array
TextDecoderDecodes a Uint8Array into a string
atobDecodes a base-64 encoded string
btoaEncodes a string in base-64
APIDescription
ReadableStreamRepresents a readable stream
WritableStreamRepresents a writable stream
WritableStreamDefaultWriterRepresents a writer of a WritableStream
TransformStreamRepresents a transform stream
ReadableStreamDefaultReaderRepresents a reader of a ReadableStream
ReadableStreamBYOBReaderRepresents a reader of a ReadableStream
APIDescription
cryptoProvides access to the cryptographic functionality of the platform
SubtleCryptoProvides access to common cryptographic primitives, like hashing, signing, encryption or decryption
CryptoKeyRepresents a cryptographic key
APIDescription
AbortControllerAllows you to abort one or more DOM requests as and when desired
AbortSignalRepresents a signal object that allows you to communicate with a DOM request (such as a Fetch request) and abort it if required
DOMExceptionRepresents an error that occurs in the DOM
structuredCloneCreates a deep copy of a value
URLPatternRepresents a URL pattern
ArrayRepresents an array of values
ArrayBufferRepresents a generic, fixed-length raw binary data buffer
AtomicsProvides atomic operations as static methods
BigIntRepresents a whole number with arbitrary precision
BigInt64ArrayRepresents a typed array of 64-bit signed integers
BigUint64ArrayRepresents a typed array of 64-bit unsigned integers
BooleanRepresents a logical entity and can have two values: true and false
clearIntervalCancels a timed, repeating action which was previously established by a call to setInterval()
clearTimeoutCancels a timed, repeating action which was previously established by a call to setTimeout()
consoleProvides access to the browser's debugging console
DataViewRepresents a generic view of an ArrayBuffer
DateRepresents a single moment in time in a platform-independent format
decodeURIDecodes a Uniform Resource Identifier (URI) previously created by encodeURI or by a similar routine
decodeURIComponentDecodes a Uniform Resource Identifier (URI) component previously created by encodeURIComponent or by a similar routine
encodeURIEncodes 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
encodeURIComponentEncodes 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
ErrorRepresents an error when trying to execute a statement or accessing a property
EvalErrorRepresents an error that occurs regarding the global function eval()
Float32ArrayRepresents a typed array of 32-bit floating point numbers
Float64ArrayRepresents a typed array of 64-bit floating point numbers
FunctionRepresents a function
InfinityRepresents the mathematical Infinity value
Int8ArrayRepresents a typed array of 8-bit signed integers
Int16ArrayRepresents a typed array of 16-bit signed integers
Int32ArrayRepresents a typed array of 32-bit signed integers
IntlProvides access to internationalization and localization functionality
isFiniteDetermines whether a value is a finite number
isNaNDetermines whether a value is NaN or not
JSONProvides functionality to convert JavaScript values to and from the JSON format
MapRepresents a collection of values, where each value may occur only once
MathProvides access to mathematical functions and constants
NumberRepresents a numeric value
ObjectRepresents the object that is the base of all JavaScript objects
parseFloatParses a string argument and returns a floating point number
parseIntParses a string argument and returns an integer of the specified radix
PromiseRepresents the eventual completion (or failure) of an asynchronous operation, and its resulting value
ProxyRepresents an object that is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc)
RangeErrorRepresents an error when a value is not in the set or range of allowed values
ReferenceErrorRepresents an error when a non-existent variable is referenced
ReflectProvides methods for interceptable JavaScript operations
RegExpRepresents a regular expression, allowing you to match combinations of characters
SetRepresents a collection of values, where each value may occur only once
setIntervalRepeatedly calls a function, with a fixed time delay between each call
setTimeoutCalls a function or evaluates an expression after a specified number of milliseconds
SharedArrayBufferRepresents a generic, fixed-length raw binary data buffer
StringRepresents a sequence of characters
SymbolRepresents a unique and immutable data type that is used as the key of an object property
SyntaxErrorRepresents an error when trying to interpret syntactically invalid code
TypeErrorRepresents an error when a value is not of the expected type
Uint8ArrayRepresents a typed array of 8-bit unsigned integers
Uint8ClampedArrayRepresents a typed array of 8-bit unsigned integers clamped to 0-255
Uint32ArrayRepresents a typed array of 32-bit unsigned integers
URIErrorRepresents an error when a global URI handling function was used in a wrong way
URLRepresents an object providing static methods used for creating object URLs
URLSearchParamsRepresents a collection of key/value pairs
WeakMapRepresents a collection of key/value pairs in which the keys are weakly referenced
WeakSetRepresents a collection of objects in which each object may occur only once
WebAssemblyProvides access to WebAssembly

You can check if your function is running on the Edge runtime by checking the global globalThis.EdgeRuntime property. This can be helpful if you need to validate that your function is running on the Edge runtime in tests, or if you need to use a different API depending on the runtime.

if (typeof EdgeRuntime !== 'string') {
  // dead-code elimination is enabled for the code inside this block
}

The following modules can be imported with and without the node: prefix when using the import statement:

ModuleDescription
async_hooksManage asynchronous resources lifecycles with AsyncLocalStorage. Supports the WinterCG subset of APIs
eventsFacilitate event-driven programming with custom event emitters and listeners. This API is fully supported
bufferEfficiently manipulate binary data using fixed-size, raw memory allocations with Buffer. Every primitive compatible with Uint8Array accepts Buffer too
assertProvide a set of assertion functions for verifying invariants in your code
utilOffer various utility functions where we include promisify/callbackify and types

Also, Buffer is globally exposed to maximize compatibility with existing Node.js nodules.

The Edge runtime has some restrictions including:

  • Some Node.js APIs other than the ones listed above 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 import instead

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

APIDescription
evalEvaluates JavaScript code represented as a string
new Function(evalString)Creates a new function with the code provided as an argument
WebAssembly.compileCompiles a WebAssembly module from a buffer source
WebAssembly.instantiateCompiles and instantiates a WebAssembly module from a buffer source

You can use process.env to access Environment Variables.

Last updated on April 18, 2024