Using Pyodide

Pyodide may be used in any context where you want to run Python inside a web browser or a backend JavaScript environment.

Web browsers

To use Pyodide on a web page you need to load pyodide.js and initialize Pyodide with loadPyodide specifying a index URL for packages:

<!DOCTYPE html>
      <script src=""></script>
    <script type="text/javascript">
      async function main(){
        let pyodide = await loadPyodide({
          indexURL : ""
        console.log(pyodide.runPython("1 + 2"));

See the Getting started for a walk through tutorial as well as Loading packages and Type translations for a more in depth discussion about existing capabilities.

You can also use the Pyodide NPM package to integrate Pyodide into your application.


To avoid confusion, note that:

  • distributes Python packages built with Pyodide as well as pyodide.js

  • is a mirror of the Pyodide NPM package, which includes none of the WASM files

Web Workers

By default, WebAssembly runs in the main browser thread, and it can make UI non responsive for long running computations.

To avoid this situation, one solution is to run Pyodide in a WebWorker.


As of version 0.18.0 Pyodide can experimentally run in Node.js.

Install the Pyodide npm package,

npm install pyodide

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

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

let pyodide_pkg = await import("pyodide/pyodide.js");

let pyodide = await pyodide_pkg.loadPyodide({
  indexURL: "<pyodide artifacts folder>",

await pyodide.runPythonAsync("1+1");


To start Node.js REPL with support for top level await, use node --experimental-repl-await.


Download of packages from PyPi is currently not cached when run in Node.js. Packages will be re-downloaded each time micropip.install is run.

For this same reason, installing Pyodide packages from the CDN is explicitly not supported for now.