Javy: A JavaScript to WebAssembly toolchain

About this repo

Introduction: Run your JavaScript on WebAssembly. Javy takes your JavaScript code, and executes it in a WebAssembly embedded JavaScript runtime.

Javy is currently used for the beta Shopify Scripts platform. We intend on supporting and improving this runtime in that context. Eventually this project should be a good general purpose JavaScript runtime but that is not the current goal.

Contributing

Javy is a beta project and will be under major development. We welcome feedback, bug reports and bug fixes. We're also happy to discuss feature development but please discuss the features in an issue before contributing. All contributors will be prompted to sign our CLA.

Build

rustup
Stable Rust (rustup install stable && rustup default stable)
wasm32-wasi, can be installed via rustup target add wasm32-wasi
cmake, depending on your operating system and architecture, it might not be installed by default. On Mac it can be installed with homebrew via brew install cmake
Rosetta 2 if running MacOS on Apple Silicon, can be installed via softwareupdate --install-rosetta
Install the wasi-sdk by running make download-wasi-sdk

Development

wasmtime-cli, can be installed via cargo install wasmtime-cli (required for cargo-wasi)
cargo-wasi, can be installed via cargo install cargo-wasi

Building

After all the dependencies are installed, run make. You should now have access to the executable in target/release/javy

Alternatively you can run make && cargo install --path crates/cli. After running the previous command you'll have a global installation of the executable.

Compiling to WebAssembly

Define your JavaScript like:

function foo(input) {
    return { foo: input.n + 1, newBar: input.bar + "!" };
}

Shopify = {
    main: foo,
};

Create a WebAssembly binary from your JavaScript by:

javy index.js -o destination/index.wasm

For more information on the commands you can run javy --help

You can then execute your WebAssembly binary using a WebAssembly engine:

$ echo '{ "n": 2, "bar": "baz" }' | wasmtime index.wasm
{"foo":3,"new_bar":"baz!"}%

Invoking Javy-generated modules programatically

Javy-generated modules are by design WASI only and follow the command pattern. Any input must be passed via stdin and any output will be placed in stdout. This is especially important when invoking Javy modules from a custom embedding.

In a runtime like Wasmtime, wasmtime-wasi can be used to set the input and retrieve the output.

Using quickjs-wasm-rs to build your own toolchain

The quickjs-wasm-rs crate that is part of this project can be used as part of a Rust crate targeting Wasm to customize how that Rust crate interacts with QuickJS. This may be useful when trying to use JavaScript inside a Wasm module and Javy does not fit your needs as quickjs-wasm-rs contains serializers that make it easier to send structured data (for example, strings or objects) between host code and Wasm code.

Releasing

Create a tag for the new version like v0.2.0

git tag v0.2.0
git push origin --tags

Create a new release from the new tag in github here.
A GitHub Action will trigger for publish.yml when a release is published (i.e. it doesn't run on drafts), creating the artifacts for downloading. However this does not currently support arm-macos, ie. M1 Macs.
Manually build this on a m1 mac

gzip -k -f target/release/javy && mv target/release/javy.gz javy-arm-macos-v0.2.0.gz

Manually create the shasum file

shasum -a 256 javy-arm-macos-v0.2.0.gz | awk '{ print $1 }' > javy-arm-macos-v0.2.0.gz.sha256

Attach both files to the new release page

nico151999/javy