Arbitraty JS at the beginning of each session

I am trying to run JS code at the beginning of a bokeh serve session and return some values to the python side which I will use later to update the plot data. Currently I am not able to see any documentation to achieve this.

I tried the following to no avail. Is there a way to do this?

from random import random
import numpy as np

from bokeh.layouts import column, row, widgetbox, layout
from bokeh.models import Button
from bokeh.palettes import RdYlBu3
from bokeh.plotting import figure, curdoc
from bokeh.models.widgets import MultiSelect, Dropdown, Select, TextInput, PreText
from bokeh.models import ColumnDataSource, CustomJS, Slider
from bokeh.models.widgets import DataTable, DateFormatter, TableColumn


source = ColumnDataSource(data=dict(x=[0,1,2]))
jscallback = CustomJS(args=dict(source=source), code="""

var data = source.get('data');
x = data['x']
x = x+x;
console.log(x)
source.trigger('change');

""")

slider = Slider(start=0.1, end=4, value=1, step=.1, title="power", callback=jscallback)

def printcallback():
    print(source.data['x'])

button1 = Button(label="Foo", button_type="success")
button1.on_click(printcallback)

l = row(slider, button1)
curdoc().add_root(l)

[bryevdv]

This capability does not yet exist.

[ImmanuelSamuel]

Ah I see yes that works however the on_change event on the source does not trigger when doing this.

In the code below moving the slider changes the source. Clicking the button shows that the source has been changed and prints out the new value. However the on change event on source is not triggered.

import numpy as np
from bokeh.layouts import column, row, widgetbox, layout
from bokeh.models import Button
from bokeh.plotting import figure, curdoc
from bokeh.models import ColumnDataSource, CustomJS, Slider


source = ColumnDataSource(data=dict(x=[0,1,2]))
def source_callback(attr, old, new):
    print(source.data['x'])
    print(new)
source.on_change('x', source_callback)


jscallback = CustomJS(args=dict(source=source), code="""
source.data = {'x': [10]}
console.log(source.data['x'])
source.trigger('change');
""")
slider = Slider(start=0.1, end=4, value=1, step=.1, title="power", callback=jscallback)


def printcallback():
    print(source.data['x'])
button1 = Button(label="Foo", button_type="success")
button1.on_click(printcallback)

l = row(slider, button1)
curdoc().add_root(l)