Overview

jco is a fully native JS tool for working with the emerging WebAssembly Components specification in JavaScript.

Features include:

• "Transpiling" Wasm Component binaries into ES modules that can run in any JS environment.
• Optimization helpers for Components via Binaryen.
• Component builds of Wasm Tools helpers, available for use as a library or CLI commands for use in native JS environments.
• "Componentize" for WebAssembly Components from JavaScript sources and a WIT world

For creating components in other languages, see the Cargo Component project for Rust and Wit Bindgen for various guest bindgen helpers.

Note: This is an experimental project, no guarantees are provided for stability or support and breaking changes may be made in future.

Installation

npm install @bytecodealliance/jco

jco can be used as either a library or as a CLI via the jco CLI command.

Example

See the example workflow page for a full usage example.

CLI

Usage: jco <command> [options]

jco - WebAssembly JS Component Tools
      JS Component Transpilation Bindgen & Wasm Tools for JS

Options:
  -V, --version                         output the version number
  -h, --help                            display help for command

Commands:
  componentize [options] <js-source>    Create a component from a JavaScript module
  transpile [options] <component-path>  Transpile a WebAssembly Component to JS + core Wasm for JavaScript execution
  run <command> [args...]               Run a WebAssembly Command component
  opt [options] <component-file>        optimizes a Wasm component, including running wasm-opt Binaryen optimizations
  wit [options] <component-path>        extract the WIT from a WebAssembly Component [wasm-tools component wit]
  print [options] <input>               print the WebAssembly WAT text for a binary file [wasm-tools print]
  metadata-show [options] [module]      extract the producer metadata for a Wasm binary [wasm-tools metadata show]
  metadata-add [options] [module]       add producer metadata for a Wasm binary [wasm-tools metadata add]
  parse [options] <input>               parses the Wasm text format into a binary file [wasm-tools parse]
  new [options] <core-module>           create a WebAssembly component adapted from a component core Wasm [wasm-tools component new]
  embed [options] [core-module]         embed the component typing section into a core Wasm module [wasm-tools component embed]
  help [command]                        display help for command

For help with individual command options, use jco <cmd> --help.

Transpile

To transpile a component into JS:

jco transpile component.wasm -o out-dir

The resultant file can be imported providing the bindings of the component as if it were imported directly:

app.js

import { fn } from './out-dir/component.js';

fn();

Imports can be remapped using the --map flag, or to provide imports as an argument use the --instantiation option.

Components relying on WASI bindings will contain external WASI imports, which are automatically updated to the @bytecodealliance/preview-shim package. This package can be installed from npm separately for runtime usage. This shim layer supports both Node.js and browsers.

Options include:

• --name: Give a custom name for the component JS file in out-dir/[name].js
• --minify: Minify the component JS
• --optimize: Runs the internal core Wasm files through Binaryen for optimization. Optimization options can be passed with a -- <binaryen options> flag separator.
• --tla-compat: Instead of relying on top-level-await, requires an $init promise to be imported and awaited first.
• --js: Converts core Wasm files to JavaScript for environments that don't even support core Wasm.
• --base64-cutoff=<number>: Sets the maximum number of bytes for inlining Wasm files into the JS using base64 encoding. Set to zero to disable base64 inlining entirely.
• --no-wasi-shim: Disable the WASI shim mapping to @bytecodealliance/preview2-shim.
• --map: Provide custom mappings for world imports. Supports both wildcard mappings (* similarly as in the package.json "exports" field) as well as # mappings for targetting exported interfaces. For example, the WASI mappings are internally defined with mappings like --map wasi:filesystem/*=@bytecodealliance/preview2-shim/filesystem#* to map import as * filesystem from 'wasi:filesystem/types' to import { types } from '@bytecodealliance/preview2-shim/filesystem.
• --no-nodejs-compat: Disables Node.js compat in the output to load core Wasm with FS methods.
• --instantiation: Instead of a direct ES module, export an instantiate function which can take the imports as an argument instead of implicit imports.
• --valid-lifting-optimization: Internal validations are removed assuming that core Wasm binaries are valid components, providing a minor output size saving.

Bindgen Crate

To directly call into the transpilation in Rust, the bindgen used in jco is also available on crates.io as js-component-bindgen.

Componentize

To componentize a JS file run:

jco componentize app.js --wit wit -n world-name -o component.wasm

Creates a component from a JS module implementing a WIT world definition, via a Spidermonkey engine embedding.

Currently requires an explicit install of the componentize-js engine via npm install @bytecodealliance/componentize-js.

See ComponentizeJS for more details on this process.

Additional engines may be supported in future via an --engine field or otherwise.

Run

For Wasm components that implement the WASI Command world, a jco run utility is provided to run these applications in Node.js:

jco run cowasy.component.wasm hello

Using the preview2-shim WASI implementation, full access to the underlying system primitives is provided, including filesystem and environment variable permissions.

Since preview2-shim is an experimental work-in-progress implementation, there will likely be bugs.

API

transpile(component: Uint8Array, opts?): Promise<{ files: Record<string, Uint8Array> }>

Transpile a Component to JS.

opt(component: Uint8Array, opts?): Promise<{ component: Uint8Array }>

Optimize a Component with the Binaryen Wasm-opt project.

componentWit(component: Uint8Array, document?: string): string

Extract the WIT world from a component binary.

print(component: Uint8Array): string

Print the WAT for a Component binary.

metadataShow(wasm: Uint8Array): Metadata

Extract the producer toolchain metadata for a component and its nested modules.

parse(wat: string): Uint8Array

Parse a compoment WAT to output a Component binary.

componentNew(coreWasm: Uint8Array | null, adapters?: [String, Uint8Array][]): Uint8Array

"WIT Component" Component creation tool, optionally providing a set of named adapter binaries.

componentEmbed(coreWasm: Uint8Array | null, wit: String, opts?: { stringEncoding?, dummy?, world?, metadata? }): Uint8Array

"WIT Component" Component embedding tool, for embedding component types into core binaries, as an advanced use case of component generation.

metadataAdd(wasm: Uint8Array, metadata): Uint8Array

Add new producer metadata to a component or core Wasm binary.

Contributing

Development is based on a standard npm install && npm run build && npm run test workflow.

Tests can be run without bundling via npm run build:dev && npm run test:dev.

Specific tests can be run adding the mocha --grep flag, for example: npm run test:dev -- --grep exports_only.

License

This project is licensed under the Apache 2.0 license with the LLVM exception. See LICENSE for more details.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be licensed as above, without any additional terms or conditions.