js_on_event

Demonstration of how to register event callbacks using an adaptation of the color_scatter example from the bokeh gallery

from __future__ import annotations

import numpy as np

from bokeh import events
from bokeh.io import curdoc, show
from bokeh.layouts import column, row
from bokeh.models import Button, CustomJS, Div, TextInput
from bokeh.plotting import figure


def display_event(div: Div, attributes: list[str] = []) -> CustomJS:
    """
    Function to build a suitable CustomJS to display the current event
    in the div model.
    """
    style = 'float: left; clear: left; font-size: 13px'
    return CustomJS(args=dict(div=div), code=f"""
        const attrs = {attributes};
        const args = [];
        for (let i = 0; i < attrs.length; i++) {{
            const val = JSON.stringify(cb_obj[attrs[i]], function(key, val) {{
                return val.toFixed ? Number(val.toFixed(2)) : val;
            }})
            args.push(attrs[i] + '=' + val)
        }}
        const line = "<span style={style!r}><b>" + cb_obj.event_name + "</b>(" + args.join(", ") + ")</span>\\n";
        const text = div.text.concat(line);
        const lines = text.split("\\n")
        if (lines.length > 35)
            lines.shift();
        div.text = lines.join("\\n");
    """)

# Follows the color_scatter gallery example

N = 4000
x = np.random.random(size=N) * 100
y = np.random.random(size=N) * 100
radii = np.random.random(size=N) * 1.5
colors = np.array([(r, g, 150) for r, g in zip(50+2*x, 30+2*y)], dtype="uint8")

p = figure(tools="pan,wheel_zoom,zoom_in,zoom_out,reset,tap,lasso_select,box_select,box_zoom,undo,redo")

p.scatter(x, y, radius=radii,
          fill_color=colors, fill_alpha=0.6,
          line_color=None)

# Add a div to display events and a button to trigger button click events

div = Div(width=1000)
button = Button(label="Button", button_type="success", width=300)
text_input = TextInput(placeholder="Input a value and press Enter ...", width=300)
layout = column(button, text_input, row(p, div))

# Register event callbacks

# Button events
button.js_on_event(events.ButtonClick, display_event(div))

# TextInput events
text_input.js_on_event(events.ValueSubmit, display_event(div, ["value"]))

# LOD events
p.js_on_event(events.LODStart, display_event(div))
p.js_on_event(events.LODEnd, display_event(div))

# Point events
point_attributes = ['x','y','sx','sy']
p.js_on_event(events.Tap,       display_event(div, attributes=point_attributes))
p.js_on_event(events.DoubleTap, display_event(div, attributes=point_attributes))
p.js_on_event(events.Press,     display_event(div, attributes=point_attributes))
p.js_on_event(events.PressUp,   display_event(div, attributes=point_attributes))

# Mouse wheel event
p.js_on_event(events.MouseWheel, display_event(div,attributes=[*point_attributes, 'delta']))

# Mouse move, enter and leave
# p.js_on_event(events.MouseMove,  display_event(div, attributes=point_attributes))
p.js_on_event(events.MouseEnter, display_event(div, attributes=point_attributes))
p.js_on_event(events.MouseLeave, display_event(div, attributes=point_attributes))

# Pan events
pan_attributes = [*point_attributes, 'delta_x', 'delta_y']
p.js_on_event(events.Pan,      display_event(div, attributes=pan_attributes))
p.js_on_event(events.PanStart, display_event(div, attributes=point_attributes))
p.js_on_event(events.PanEnd,   display_event(div, attributes=point_attributes))

# Pinch events
pinch_attributes = [*point_attributes, 'scale']
p.js_on_event(events.Pinch,      display_event(div, attributes=pinch_attributes))
p.js_on_event(events.PinchStart, display_event(div, attributes=point_attributes))
p.js_on_event(events.PinchEnd,   display_event(div, attributes=point_attributes))

# Ranges Update events
p.js_on_event(events.RangesUpdate, display_event(div, attributes=['x0','x1','y0','y1']))

# Selection events
p.js_on_event(events.SelectionGeometry, display_event(div, attributes=['geometry', 'final']))

curdoc().on_event(events.DocumentReady, display_event(div))

show(layout)