Starlark interpreter for Javascript using WebAssembly

Usage

$ npm install starlark-webasm

import { initialize } from 'starlark-webasm';

const starlark_code = `
def main():
    print("hello world")
`;

async function main() {
    await initialize();
    const result = run_starlark_code(starlark_code);
    if(result.error) return console.error(result.error);
    console.log(result.message);
}

main();

Overview

NPM package https://www.npmjs.com/package/starlark-webasm

See it running at https://haribala.dev/starlark-webasm-demo

This library adds a function called run_starlark_code to the window object (globals).

Starlark is a Python-like language.
It runs in a sandbox, meaning it does not have access to the file system, the network, the current time, sources of randomness, etc. This makes it very safe to run unsafe user provided code because the Starlark code can only access stuff that we explicitly give it access to.

Starlark An overview of the language.
Starlark Language Specification Detailed reference spec.
starlark-go A Starlark interpreter written in Golang.

This interpreter and some wrapper code (see main.go) are compiled into a WASM binary.
The javascript code in src/index.js exports a function called initialize that fetches the WASM module at runtime and compiles it.
The WASM code adds a javascript function called run_starlark_code which accepts Starlark source code and returns an object.
The object returned by run_starlark_code will have a field called error containing an error message OR
it will have a field called message which contains the result of running the Starlark code.
The output of all the print function calls in the Starlark code is returned as the result.