`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)

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