When writing an anywidget use vanilla javascript in
and do not forget about
. The css should look bespoke in light mode and dark mode. Keep the css small unless explicitly asked to go the extra mile. When you display the widget it must be wrapped via
widget = mo.ui.anywidget(OriginalAnywidget())
. You can also point
and
to external files if needed using pathlib. This makes sense if the widget does a lot of elaborate JavaScript or CSS.
<example title="Example of simple anywidget implementation">
import anywidget
import traitlets
class CounterWidget(anywidget.AnyWidget):
_esm = """
// Define the main render function
function render({ model, el }) {
let count = () => model.get("number");
let btn = document.createElement("b8utton");
btn.innerHTML =
;
btn.addEventListener("click", () => {
model.set("number", count() + 1);
model.save_changes();
});
model.on("change:number", () => {
btn.innerHTML =
;
});
el.appendChild(btn);
}
// Important! We must export at the bottom here!
export default { render };
"""
_css = """button{
font-size: 14px;
}"""
number = traitlets.Int(0).tag(sync=True)
The above is a minimal example that could work for a simple counter widget. In general the widget can become much larger because of all the JavaScript and CSS required. Unless the widget is dead simple, you should consider using external files for
and
using pathlib.
When sharing the anywidget, keep the example minimal. No need to combine it with marimo ui elements unless explicitly stated to do so.
-
Use vanilla JavaScript in :
- Define a function that takes as parameters
- Use to read trait values
- Use and to update traits
- Listen to changes with
model.on("change:traitname", callback)
- Export default with
export default { render };
- All widgets inherit from , so
remains the standard way to react to state changes.
- Python constructors tend to validate bounds, lengths, or choice counts; let the
raised guide you instead of duplicating the logic.
-
- Keep CSS minimal unless explicitly asked for more
- Make it look bespoke in both light and dark mode
- Use CSS media query for dark mode:
@media (prefers-color-scheme: dark) { ... }
-
Wrap the widget for display:
- Always wrap with marimo:
widget = mo.ui.anywidget(OriginalAnywidget())
- Access values via which returns a dictionary
-
Keep examples minimal:
- Add a marimo notebook that highlights the core utility
- Show basic usage only
- Don't combine with other marimo UI elements unless explicitly requested
Dumber is better. Prefer obvious, direct code over clever abstractions—someone
new to the project should be able to read the code top-to-bottom and grok it
without needing to look up framework magic or trace through indirection.