Support the Anywidget Front-End Module specification

[azjps]

Motivation: The set of published widgets using anywidget is growing and includes a few established plotting libraries such as plotly.FigureWidget and altair.JupyterChart (example request thread: #657; other examples of published anywidgets). I think its the recommended way to publish custom widgets for marimo, and maybe jupyter too. I'm personally using anywidget to render a couple of custom widgets in Jupyter/Marimo & Panel, and it would be nice to be able to directly take them and use them in nicegui.

Details: https://anywidget.dev/en/afm/#what-is-afm AFM describes the basic contract for front-end frameworks to support anywidgets, namely calling render({model, el}) to create a widget and implementing the model.get/set/save_changes() API to synchronize state with the backend. On the python side, anywidgets are traitlets.HasTraits with syncable properties tagged as sync=True (analogous to nicegui.binding.BindableProperty), although there are some experimental internal helpers for adding widget MIME bundles to any popular dataclass-like API, e.g. dataclass/pydantic/msgspec.

In practice there's likely a few options to support this:

• Support ipywidgets: For example, this is the approach of the ipywidgets_bokeh project used by bokeh & panel. Pros: anywidget is (currently) just an ipywidget; other ipywidgets elements could be supported too. Cons: ipywidgets is relatively heavy; would have to hook into the internals of the jupyter-widgets extension module; there's little documentation on the internals but at least there is this ipywidgets-bokeh example to follow.
• Sync the model state via the synced traits in traitlets.HasTraits: For example, this is the approach of streamlit-anywidget: iterate HasTraits.traits(sync=True) to get a widget_state json dict, sync it to JS via streamlit's components API, implement the model API here using streamlit's websockets API to sync changes to widget_state back to python. [Note that this streamlit-anywidget is a community extension and misses a few features, for example it currently doesn't support the traits_to_json serialization escape-hatch from ipywidgets, or specifying _esm as a Path.] I guess this would probably be the easiest approach, using bindings in place of streamlit's components?
• Support the experimental MIME bundle descriptor and use the corresponding anywidgets helper APIs to get the widget state, and the comm bridge to handle 2-way state communication. Pros: not tied to traitlets. Cons: experimental and I believe its a hidden API at the moment.

Other details on integrating the JavaScript and comms side with nicegui are completely beyond me, but I'm sure the anywidgets maintainers would be happy to provide advice. Also please note these suggestions are just from a quick skim of existing projects I'm aware of, I have no development experience here beyond being a happy end-user.

[falkoschindler]

Thanks for sharing this interesting idea, @azjps! Anywidget could indeed make NiceGUI more accessible for an even wider audience.

To me an integration doesn't seem trivial to implement though. But maybe someone from the community would like to give it a go? Some sketchy proof of concept might be enough to pave the way. 🤞🏻