jsco - Browser polyfill for running WASM components

Demo

See live demo and browser demo sources

Goals

• browser polyfill for running WASM components.
• streaming parser of binary WIT
• streaming compilation of WASM module during .wasm file download
• in-the-browser creation of instances and necessary JavaScript interop
• small download size, fast enough (current prototype is 35 KB)

How

• parser: read binary WIT to produce model of the component, it's sub components, modules and types
• compile modules via Browser API WebAssembly.compileStreaming
• resolver: resolve dependencies, create instances, bind it together.
• JS binding: for component's imports and exports
• just JS (no rust dependency), TypeScript, RollupJS

Status

🚧 This is demo-ware quality right now: There are still few things hardcoded and fake 🚧

🚧 Parser: 90%, Resolver: 50%, Lifting/Lowering: 5% 🚧

See ./TODO.md, contributors are welcome!

Demo scope

• hello world demo hello.wit hello.wat lib.rs
• this is just small attempt in limited time. It may grow into something larger ...
• binding for string and i32, record just one direction. Only necessary resolver.
• as a hackathon week project in 2023
• to learn more about WASM component model

Why

• to provide host which could do the binding in the browser
• browsers currently don't implement built-in WASM component model host
• because independent implementation will help the WASM/WIT/WASI to make progress
• JCO is great alternative, really.
  • But it is too large to use as dynamic host, because download size matters to browser folks.
  • When you have all your components available at dev machine, JCO transpiler could be better choice.

Usage

import { instantiateComponent } from '@pavelsavara/jsco';
const instance = await instantiateComponent('./hello/wasm/hello.wasm', {
    'hello:city/city': { sendMessage: console.log }
});
const run = instance.exports['hello:city/greeter'].run;
run({ name: 'Kladno', headCount: 100000, budget: 0n});

Prints Welcome to Kladno! to the console.

See ./usage.mjs for full commented sample.

Contribute

• install rust
• install nodejs + npm
• use eslint plugin to VS code, with format on save
• see "scripts" in package.json

npm install
npm run setup:rust
npm run build
npm run build:hello && npm run build:hello-wat && npm run build:hello-js
npm run test:jco
npm run test:unix