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
  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

Componentize

To componentize a JS file run:

jco componentize app.js --wit world.wit -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.

API

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

Transpile a Component to JS.

Transpilation options:

• name?: string - name for the generated JS file.
• instantiation?: bool - instead of a direct ES module, output the raw instantiation function for custom virtualization.
• map?: Record<string, string> - remap component imports
• validLiftingOptimization?: bool - optimization to reduce code size
• noNodejsCompat?: bool - disables Node.js compatible output
• tlaCompat?: bool - enable compat in JS runtimes without TLA support
• base64Cutoff?: number - size in bytes, under which Wasm modules get inlined as base64.
• js?: bool - convert Wasm into JS instead for execution compatibility in JS environments without Wasm support.
• minify?: bool - minify the output JS.
• optimize?: bool - optimize the component with Binaryen wasm-opt first.
• optArgs?: string[] - if using optimize, custom optimization options (defaults to best optimization, but this is very slow)

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.