Starlark in the Browser

A typescript library for running starlark-go in the browser using WebAssembly.

npm install starlark-wasm

Example

import { Starlark } from "starlark-wasm";
import wasmUrl from "starlark-wasm/wasm?url";

const exampleCode = `
def hello_world(name):
    print("hello " + name)
    return 42`;

// load the wasm module
Starlark.init(wasmUrl);

// instantiate a new starlark runtime, defining a load and print function
const starlark = new Starlark({
  // load gives you module loading
  load: async (filename) => {
    const files = {
      "main.star": exampleCode,
    };
    return files[filename];
  },

  // print to a console
  print: (message) => {
    console.log(message);
  },
});

const returnValue = await starlark.run(
  "main.star", // the file to run
  "hello_world", // the function to call
  ["starlark"], // the args for the function
  {}, // the kwargs for the function
  1 // maximum execution seconds before timeout
);

Project Structure

• index.html: A demo of using this library, running starlark in the browser
• go/: The go code that compiles to starlark.wasm
• public/: Where starlark.wasm lives. Note: this is to be hosted and included as an asset in your project
• src/: The typescript project

Implementation details

The WebAssembly code adds a wasm_runner function a window.starlark global. This global object also has the underlying print and load functions which wasm_runner calls during execution. Calling run on a Starlark instance also registers an execution thread with this global object, so that when the underlying load and print functions are called, they can invoke the respective functions on the relevant instance. This allows you to set up multiple runtimes/projects and call starlark functions on them independently, e.g. loading from different file structures or printing to different consoles.

Building

1. Build starlark.wasm

   npm run build-go

2. Build the typescript project

   npm run build

3. Run the demo

   npm run dev

Credits

Borrowed concepts and inspiration from https://github.com/HarikrishnanBalagopal/starlark-webasm