https://github.com/bytecodealliance/javy

JS to WebAssembly toolchain
https://github.com/bytecodealliance/javy

Last synced: 4 days ago
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JS to WebAssembly toolchain

• Host: GitHub
• URL: https://github.com/bytecodealliance/javy
• Owner: bytecodealliance
• License: apache-2.0
• Created: 2021-04-22T13:36:40.000Z (almost 4 years ago)
• Default Branch: main
• Last Pushed: 2025-01-08T21:25:06.000Z (17 days ago)
• Last Synced: 2025-01-14T14:08:27.651Z (11 days ago)
• Language: Rust
• Size: 101 MB
• Stars: 2,343
• Watchers: 248
• Forks: 115
• Open Issues: 28
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.md
  • Code of conduct: CODE_OF_CONDUCT.md

Awesome Lists containing this project

• awesome-ccamel - bytecodealliance/javy - JS to WebAssembly toolchain (Rust)

README

        


  
Javy


  


    A JavaScript to Webassembly toolchain

  


  A Bytecode Alliance project

  


    

    

  



## About this repo

**Introduction**: Run your JavaScript on WebAssembly. Javy takes your JavaScript

code, and executes it in a WebAssembly embedded JavaScript runtime. Javy can

create _very_ small Wasm modules in the 1 to 16 KB range with use of dynamic

linking. The default static linking produces modules that are at least 869 KB in

size.

## Installation

Pre-compiled binaries of the Javy CLI can be found on [the releases

page](https://github.com/bytecodealliance/javy/releases).

## Example

Define your JavaScript like:

```javascript

// Read input from stdin

const input = readInput();

// Call the function with the input

const result = foo(input);

// Write the result to stdout

writeOutput(result);

// The main function.

function foo(input) {

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

}

// Read input from stdin

function readInput() {

    const chunkSize = 1024;

    const inputChunks = [];

    let totalBytes = 0;

    // Read all the available bytes

    while (1) {

        const buffer = new Uint8Array(chunkSize);

        // Stdin file descriptor

        const fd = 0;

        const bytesRead = Javy.IO.readSync(fd, buffer);

        totalBytes += bytesRead;

        if (bytesRead === 0) {

            break;

        }

        inputChunks.push(buffer.subarray(0, bytesRead));

    }

    // Assemble input into a single Uint8Array

    const { finalBuffer } = inputChunks.reduce((context, chunk) => {

        context.finalBuffer.set(chunk, context.bufferOffset);

        context.bufferOffset += chunk.length;

        return context;

    }, { bufferOffset: 0, finalBuffer: new Uint8Array(totalBytes) });

    return JSON.parse(new TextDecoder().decode(finalBuffer));

}

// Write output to stdout

function writeOutput(output) {

    const encodedOutput = new TextEncoder().encode(JSON.stringify(output));

    const buffer = new Uint8Array(encodedOutput);

    // Stdout file descriptor

    const fd = 1;

    Javy.IO.writeSync(fd, buffer);

}

```

Create a WebAssembly binary from your JavaScript by:

```bash

javy build 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:

```bash

$ echo '{ "n": 2, "bar": "baz" }' | wasmtime index.wasm

{"foo":3,"newBar":"baz!"}%   

```

## Documentation

Read the documentation [here](./docs/index.md)