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    0.21.3 • Public • Published

    Pyodide JavaScript package



    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 initialization complete
    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");
    > let pyodide = await loadPyodide();
    Loading distutils
    Loaded distutils
    Python initialization complete
    > await pyodide.runPythonAsync("1+1");

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

    See the documentation fore more details.


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

    1. Defines the public JavaScript API
      • Package loading code to allow loading of other Python packages.
      • Can load micropip to bootstrap loading of pure Python wheels
    2. Loads the CPython interpreter and the core/pyodide emscripten application which embeds the interpreter.
    3. 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.


    npm i pyodide

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    • hoodmane
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