marker keyword does not work for TimeLine class

[LeResch]

Describe the bug
I tried to change the marker of the features of a TimeLine object. The GeoJSON input data only contains Point geometries.
Since TimeLine should base on GeoJSON class, I tried using the marker keyword in the timeline. The python code runs without an error, but when I try to open the map in the browser I get the following error:

Uncaught ReferenceError: circle_edc1a78feb8824a28fc2c53a5e766edf is not defined
at folium_ywd748p8.html:102:13
So apparently the circle referenced by the timeline_options is not created.

To Reproduce

import geopandas as gpd
from datetime import datetime
import folium
from folium.plugins import Timeline, TimelineSlider

data = gpd.read_file("https://raw.githubusercontent.com/python-visualization/folium-example-data/main/subway_stations.geojson")
data["start"] = (datetime.strptime("01.01.2025", "%d.%m.%Y")).timestamp()*10e2
data["end"] = (datetime.strptime("01.01.2026", "%d.%m.%Y")).timestamp()*10e2
m = folium.Map()
timeline = Timeline(
    data=data,
    marker = folium.Circle(radius=3, color="black")
).add_to(m)
TimelineSlider(
    auto_play=False,
    show_ticks=True,
    enable_keyboard_controls=True,
    start = (datetime.strptime("01.01.2024", "%d.%m.%Y")).timestamp()*10e2
).add_timelines(timeline).add_to(m)

m.show_in_browser() 

Expected behavior
I would except that when the timeline class is based on the GeoJSON class, that I can change the marker for Point geometries with the marker keyword. The marker also needs to be created, when the map object is rendered to html.

Environment (please complete the following information):

• Browser: MS Edge Version 131.0.2903.86
• Python version: 3.9.7
• folium version: 0.19.4
• branca version: 0.8.1

[hansthen]

I see your point. Unfortunately, the current implementation of Timeline and GeoJson make it really hard to do this the exact way you want.

There is a workaround. You can customize the marker for the layer by customizing the Javascript point_to_layer function:

timeline = Timeline(
    data=data,
    point_to_layer=JsCode("(f, latlng) => { return L.circleMarker(latlng, {radius: 8, fillOpacity: 0.2})}")
).add_to(m)

Can you check if that works out for you?

[LeResch]

Okay, understood.
The workaround is working fine for me, thank you for providing that. I think in combination with the style_function there are hardly any or no restrictions, so I'll close this bug.