Convert JavaScript source code into WebAssembly components using QuickJS.

componentize-qjs takes a JavaScript source file and a WIT definition, and produces a standalone WebAssembly component that can run on any component-model runtime (e.g. Wasmtime).

Under the hood it:

1. Embeds the QuickJS engine (via rquickjs) as the JavaScript runtime.
2. Uses wit-dylib to generate WIT bindings that bridge the component model and the JS engine.
3. Snapshots the initialized JS state with Wizer so startup cost is paid at build time, not at runtime.

Building currently requires a nightly Rust toolchain because it relies on the wasi-libc being compiled with -fPIC. This requirement will be lifted with an upcoming version of Rust.

cargo +nightly install --path .

The npm package is not yet published to the registry. To use it, build from source:

cd npm && npm install && npm run build

1. Define a WIT interface (hello.wit):

package test:hello;

world hello {
    export greet: func(name: string) -> string;
}

2. Implement it in JavaScript (hello.js):

function greet(name) {
    return `Hello, ${name}!`;
}

3. Build the component:

componentize-qjs --wit hello.wit --js hello.js -o hello.wasm

4. Run it:

wasmtime run --invoke 'greet("World")' hello.wasm
# Hello, World!

componentize-qjs [OPTIONS] --wit <WIT> --js <JS>

Build with features:

cargo +nightly build --release --features optimize-size

WIT imports are available on globalThis keyed by their fully-qualified name:

// imports.wit
package local:test;

interface math {
    add: func(a: s32, b: s32) -> s32;
    multiply: func(a: s32, b: s32) -> s32;
}

world imports {
    import math;
    export double-add: func(a: s32, b: s32) -> s32;
}

// imports.js
function doubleAdd(a, b) {
    const math = globalThis["local:test/math"];
    const sum = math.add(a, b);
    return math.multiply(sum, 2);
}

The npm package exposes both a CLI and a programmatic API. It is not yet published to the registry — see Installation for building from source.

./npm/bin/componentize-qjs --wit hello.wit --js hello.js -o hello.wasm

import { componentize } from "componentize-qjs";

const { component } = await componentize({
    witPath: "hello.wit",
    jsSource: "function greet(name) { return `Hello, ${name}!`; }",
});
// component is a Buffer containing the WebAssembly component bytes

This project builds on ideas and code from:

• ComponentizeJS by Joel Dice
• lua-component-demo by Alex Crichton

Licensed under Apache-2.0.