This is the mirror image of #2170.

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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- [x] Add new / update outdated documentation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
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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- [x] Add new / update outdated documentation

---
name: Feature request
about: Suggest an idea for Pyodide
title: ""
labels: enhancement
assignees: ""
---

## 🚀 Feature

<!-- A clear and concise description of the feature proposal -->

### Motivation

<!-- Please outline the motivation for the proposal. Is your feature request related to a problem? e.g., I'm always frustrated when [...]. If this is related to another GitHub issue, please link here too -->

### Pitch

<!-- A clear and concise description of what you want to happen. -->

### Alternatives

<!-- A clear and concise description of any alternative solutions or features you've considered, if any. -->

### Additional context

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---
name: Feature request
about: Suggest an idea for Pyodide
title: ""
labels: enhancement
assignees: ""
---

## 🚀 Feature

<!-- A clear and concise description of the feature proposal -->

### Motivation

<!-- Please outline the motivation for the proposal. Is your feature request related to a problem? e.g., I'm always frustrated when [...]. If this is related to another GitHub issue, please link here too -->

### Pitch

<!-- A clear and concise description of what you want to happen. -->

### Alternatives

<!-- A clear and concise description of any alternative solutions or features you've considered, if any. -->

### Additional context

<!-- Add any other context or screenshots about the feature request here. -->
