WinterJS is blazing-fast JavaScript server that runs Service Workers scripts according to the Winter Community Group specification.

WinterJS is able to handle up to 100,000 reqs/s in a single laptop (see Benchmark).

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Note: WinterJS is not officially endorsed by WinterCG, despite sharing "Winter" in their name. There are many runtimes supporting WinterCG, WinterJS being one among those.

Running WinterJS with Wasmer

The WinterJS server is published in Wasmer as wasmer/winterjs.

You can run the HTTP server locally with:

wasmer run wasmer/winterjs --net --mapdir=tests:tests tests/simple.js

Where simple.js is:

addEventListener('fetch', (req) => {
  req.respondWith(new Response('hello'));
});

Running WinterJS Natively

You can install WinterJS natively with:

cargo install --git https://github.com/wasmerio/winterjs

Once you have WinterJS installed, you can simply do:

winterjs tests/simple.js

And then access the server in https://localhost:8080/

How WinterJS works

WinterJS is powered by SpiderMonkey, Spiderfire and hyper to bring a new level of awesomeness to your Javascript apps.

WinterJS is using the WASIX standard to compile to WebAssembly. Please note that compiling to WASIX is currently a complex process. We recommend using precompiled versions from wasmer/winterjs, but please open an issue if you need to compile to WASIX locally.

Limitations

WinterJS is fully compliant with the WinterCG spec, although the runtime itself is still a work in progress. For more information, see the API Compatibility section below.

WinterCG API Compatibility

This section will be updated as APIs are added/fixed. If an API is missing from this section, that means that it is still not implemented.

The following words are used to describe the status of an API:

• ✅ Stable - The API is implemented and fully compliant with the spec. This does not account for potential undiscovered implementation errors in the native code.
• 🔶 Partial - The API is implemented but not fully compliant with the spec and/or there are known limitations.
• ❌ Pending - The API is not implemented yet.

API	Status	Notes
console	✅ Stable
fetch	✅ Stable
URL	✅ Stable
URLSearchParams	✅ Stable
Request	✅ Stable
Headers	✅ Stable
Response	✅ Stable
Blob	✅ Stable
File	✅ Stable
FormData	✅ Stable
TextDecoder	✅ Stable
TextDecoderStream	✅ Stable
TextEncoder	✅ Stable
TextEncoderStream	✅ Stable
ReadableStream and supporting types	✅ Stable
WritableStream and supporting types	✅ Stable
TransformStream and supporting types	🔶 Partial	Back-pressure is not implemented
atob	✅ Stable
btoa	✅ Stable
performance.now()	✅ Stable
performance.timeOrigin	✅ Stable
crypto	✅ Stable
crypto.subtle	🔶 Partial	Only HMAC, MD5 and SHA algorithms are supported

Other supported APIs

The following (non-WinterCG) APIs are implemented and accessible in WinterJS:

API	Status	Notes
Service Workers Caches API	✅ Stable	Accessible via caches. caches.default (similar to Cloudflare workers) is also available. The current implementation is memory-backed, and cached responses will not persist between multiple runs of WinterJS.