This is the mirror image of #2170.

### Checklists

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- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

Add `default_converter` argument to `to_js` and `toJs`. This is the mirror image of #2170.

### Checklists

<!-- Note on checklists:
     If you think some of these steps are not necessary for your PR,
     just remove those checkboxes, or mark them as checked. Otherwise,
     if some checkboxes are left unmarked, we might assume that your PR
     is not ready to be merged and we might keep you waiting -->

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

# Pyodide JavaScript package

<a href="https://www.npmjs.com/package/pyodide"><img src="https://img.shields.io/npm/v/pyodide" alt="npm"></a>

## Usage

Download and extract Pyodide packages from [Github
releases](https://github.com/pyodide/pyodide/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,

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

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

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

**Note**: To start node REPL with support for top level await, use `node --experimental-repl-await`.

See the [documentation](https://pyodide.org/en/stable/) fore more details.

## Details

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

1. Defines the public [JavaScript API](https://pyodide.org/en/stable/usage/api/js-api.html)
   - Package loading code to allow loading of other Python packages.
   - Can load
     [micropip](https://pyodide.org/en/stable/usage/api/micropip-api.html) 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.

# Pyodide JavaScript package

<a href="https://www.npmjs.com/package/pyodide"><img src="https://img.shields.io/npm/v/pyodide" alt="npm"></a>

## Usage

Download and extract Pyodide packages from [Github
releases](https://github.com/pyodide/pyodide/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,

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

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

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

**Note**: To start node REPL with support for top level await, use `node --experimental-repl-await`.

See the [documentation](https://pyodide.org/en/stable/) fore more details.

## Details

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

1. Defines the public [JavaScript API](https://pyodide.org/en/stable/usage/api/js-api.html)
   - Package loading code to allow loading of other Python packages.
   - Can load
     [micropip](https://pyodide.org/en/stable/usage/api/micropip-api.html) 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.
