Pyodide JavaScript package

Usage

Download and extract Pyodide packages from Github releases (pyodide-build-*.tar.bz2). The version of the release needs to match exactly the version of this package.

Then you can load Pyodide in Node.js as follows,

// hello_python.js
const { loadPyodide } = require("pyodide");

async function hello_python() {
  let pyodide = await loadPyodide({
    indexURL: "<pyodide artifacts folder>",
  });
  return pyodide.runPythonAsync("1+1");
}

hello_python().then((result) => {
  console.log("Python says that 1+1 =", result);
});

$ node hello_python.js
Loading distutils
Loaded distutils
Python says that 1+1= 2

Or you can use the REPL. To start the Node.js REPL with support for top level await, use node --experimental-repl-await:

$ node --experimental-repl-await
Welcome to Node.js v18.5.0.
Type ".help" for more information.
> const { loadPyodide } = require("pyodide");
undefined
> let pyodide = await loadPyodide();
Loading distutils
Loaded distutils
undefined
> await pyodide.runPythonAsync("1+1");
2

Node.js versions <0.17

• Node.js versions 14.x and 16.x: to use certain features of Pyodide you need to manually install node-fetch, e.g. by doing npm install node-fetch.

• Node.js v14.x: you need to pass the option --experimental-wasm-bigint when starting Node. Note that this flag is not documented by node --help and moreover, if you pass --experimental-wasm-bigint to node >14 it is an error:

$ node -v
v14.20.0

$ node --experimental-wasm-bigint hello_python.js
warning: no blob constructor, cannot create blobs with mimetypes
warning: no BlobBuilder
Loading distutils
Loaded distutils
Python says that 1+1= 2

See the documentation fore more details.

Details

The JavaScript code in this package is responsible for the following tasks:

1. Defines the public JavaScript API
2. Package loading code to allow loading of other Python packages.
3. Can load micropip to bootstrap loading of pure Python wheels
4. Loads the CPython interpreter and the core/pyodide emscripten application which embeds the interpreter.
5. Injects the js/pyodide JavaScript API into sys.modules. This is the final runtime dependency for core/pyodide & py/pyodide, so after this step the interpreter is fully up and running.