Bokeh Taptool return selected index

Question

I need to get the index of a selected data point in a Bokeh plot, which needs to be the input of another function in my web application.

I am using Bokeh's Taptool CustomJS Callback. However, I could not find a way to get the actual index of the selected point besides 'console.log'. Is there some way to return this index to outside the JavaScript?

Below is my code. I am new to Javascript and Bokeh. Thanks for any help in advance.

codes = """
    var index_selected = source.selected['1d']['indices'][0];
    source.trigger('change');

    console.log(index_selected);
    """
taptool.callback = CustomJS(args=dict(source=source),code = codes)

Answer 1

This works with multi_line:

selected_src = ColumnDataSource(dict(indices=[])

def handle_selection_change(_attr, # should be 'data'
                            old_indices, 
                            new_indices):
   ...

selected_src.on_change('data', handle_selection_change)

taptool.callback = CustomJS(
    args=dict(source=source, selected=selected_src),
    code = """
       selected.data = { "indices" : source.selected.indices };
    """)