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EAS Hosting worker runtime

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

Caching with API Routes

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 CG, 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 shim modules

The list of compatibility modules for Node.js APIs natively supported by Cloudflare's runtime are:

  • assert
  • async_hooks
  • buffer
  • crypto (With some limitations and missing exports)
  • diagnostics_channel
  • events
  • path, path/posix, and path/win32
  • process
  • querystring
  • stream, stream/consumers, stream/promises, and stream/web
  • string_decoder
  • url
  • util
  • zlib

Additionally, EAS Hosting provides JavaScript-level shims (or rather polyfills) for the following modules:

  • http
  • https
  • tty

These modules generally provide a lower-accuracy polyfill 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.

The following modules are mocked but won't provide any functionality:

  • child_process
  • net

Any of the above Node.js modules can be used in API routes or dependencies of your API routes as usual and will use appropriate compatibility modules.

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

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

Globals

  • The process global is present with mock values set as appropriate to match Node.js
  • process.env is available and will be populated with your deployment's environment variables
  • process.stdout and process.stderr will convert the output written to them to console.log and console.error calls
  • setImmediate and clearImmediate are available as shims around setTimeout and clearTimeout
  • The Buffer and EventEmitter globals are available and set to their Node.js shims
  • global is available and set to globalThis
  • require() is available in CommonJS modules but require.cache is unavailable