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.
Pre-compiled binaries of the Javy CLI can be found on the releases page.
Define your JavaScript like:
// 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:
javy build index.js -o destination/index.wasmFor 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,"newBar":"baz!"}% Read the documentation here