EAS Hosting worker runtime

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Learn about EAS Hosting worker runtime and Node.js compatibility.


EAS Hosting is built on Cloudflare Workers, a modern and powerful platform for serverless APIs that's been built for seamless scalability, high reliability, and exceptional performance globally.

The Cloudflare Workers runtime runs on the V8 JavaScript engine, the same powering JavaScript in Node.js and Chromium. However, its runtime has a few key differences from what you might be used to in traditional serverless Node.js deployments.

Instead of each request running in a full JavaScript process, Workers are designed to run them in small V8 isolates, a feature of the V8 runtime. Think of them as micro-containers in a single JavaScript process.

For more information on how Workers work, see Cloudflare Workers documentation.

Node.js compatibility

Cloudflare is part of Winter TC, is more similar to the JavaScript environments in browsers and service workers rather than in Node.js. Restrictions like these provide a leaner runtime than Node.js, which is still familiar. This common runtime is a minimal standard supported by many JavaScript runtime these days.

This means, many Node.js APIs that you might be used to or some dependencies you utilize, aren't directly available in the EAS Hosting runtime. To ease this transition, as not all dependencies will have first-class support for Web APIs yet, Node.js compatibility modules exist and can be used in your API routes.

Node.js built-in moduleSupportedImplementation notes
node:assert
node:async_hooks
node:buffer
node:cryptoSelect deprecated algorithms are not available
node:consoleProvided as partially functional JS shims
node:constants
node:diagnostics_channelSelect deprecated algorithms are not implemented
node:dnsResolver is unimplemented, all DNS requests are sent to Cloudflare
node:dns/promisesAll DNS requests are sent to Cloudflare
node:events
node:fsProvided as JS stubs, since workers have no file system
node:fs/promisesProvided as JS stubs, since workers have no file system
node:httpProvided as partially functional JS shims based on fetch
node:httpsProvided as partially functional JS shims based on fetch
node:moduleSourceMap is unimplemented, partially supported otherwise
node:netServer and BlockList are unimplemented, client sockets are partially supported
node:osProvided as JS stubs that provide mock values matching Node.js on Linux
node:path
node:path/posix
node:path/win32
node:processProvided as JS stubs
node:punycode
node:querystring
node:readlineProvided as non-functional JS stubs, since workers have no stdin
node:readline/promisesProvided as non-functional JS stubs, since workers have no stdin
node:stream
node:stream/consumers
node:stream/promises
node:stream/web
node:string_decoder
node:timers
node:timers/promises
node:tlsProvides JS stubs but is unimplemented
node:trace_eventsProvided as non-functional JS stubs
node:ttyProvided as JS shims redirecting output to the Console API
node:url
node:util
node:util/types
node:worker_threadsProvided as non-functional JS stubs, since workers don't support threading
node:zlib

These modules generally provide a lower-accuracy polyfill or approximation of their Node.js counterparts. For example, the http and https modules only provide thin Node.js compatibility wrappers around the fetch API and cannot be used to make arbitrary HTTP requests.

Any of the above listed Node.js modules can be used in API routes or dependencies of your API routes as usual and will use appropriate compatibility modules. However, some of these modules may not provide any practical functionality and only exist to shim APIs to prevent runtime crashes.

Any modules that aren't mentioned here are unavailable or unsupported, and your code and none of your dependencies should rely on them being provided.

More Node.js compatibility shims may be added in the future, but all Node.js APIs that are not documented in this non-exhaustive list are not expected to work.

Globals

JavaScript runtime globalsSupportedImplementation notes
process
process.envPopulated with EAS Hosting environment variables
process.stdoutWill redirect output to the Console API (console.log) for logging
process.stderrWill redirect output to the Console API (console.error) for logging
setImmediate
clearImmediate
BufferSet to Buffer from node:buffer
EventEmitterSet to EventEmitter from node:events
globalSet to globalThis
WeakRefShim that resets references after each request
FinalizationRegistryGarbage collection is not observable within workers
requireExternal requires are supported but limited to deployed JS files and built-in modules. Node module resolution is unsupported.
require.cache