[BUG] Unable to update plot.title in BokehJS

[oviquezr]

Version info

bokeh-*-2.2.3.js, including bokeh-api

Description of expected behavior and the observed behavior

• plot.title = "new title" fails to update rendered title
• the instruction does update the object records as scoped via console
• changingplot.title_location doesn't move title as expected (see caveat)

A caveat to these two behaviors:

• the title_location change does eventually move the text to its new location after using plot.width = <new width> to resize the plot.
• the rendered title does not update to the new string when using the same process to try triggering the update.

Self-contained example code

Relates to:

• Discourse : How to update a title from bokehJS
• jsfiddle : example code by PBrockmann

Expand on the BokehJS Minimal Example by adding the following to the end of the script, after the two calls to addPoint(); :

function addTitle() {
    // add [new title]
    console.log(plot.title)
    plot.title = plot.title+'1';
    console.log(plot.title)

    // notify the [plot object] of "in-place" changes
    // after initial failures, tried calling plot.change.emit() thinking to mimic 
    // the source.change.emit() used for updating ColumnDataSource
    plot.change.emit()
}


var addDataButton2 = document.createElement("Button");
addDataButton2.appendChild(document.createTextNode("Add Some Text!!!"));
document.currentScript.parentElement.appendChild(addDataButton2);
addDataButton2.addEventListener("click", addTitle);

Stack traceback and/or browser JavaScript console output

Pressing the button to change the title logs the following to console:

Example of Random data
Example of Random data1

[bryevdv]

Plot titles are objects, not simple strings. You have to change plot.title.text = "new title" (in fact this is exactly what was demonstrated in the links above). As a gentle suggestion, please consider visiting the community support forums first in cases where it is not 100% certain something is a bug. If something is determined to be a bug we will recommend opening an issue with details.

[oviquezr]

The title certainly behaves as an object in Python, where I can change plot.title.text = "new title" without issue.
However, I'm trying to do this with BokehJS alone, where I get that var plot = Bokeh.Plotting.figure(title="some title") yields:

typeof plot.title
"string"
typeof plot.title.text
"undefined"

I tried assigning a Title() object instead of a string when creating the plot, but I got no title rendered in that scenario.

[bryevdv]

@oviquezr evidently the JS side handles plain string init differently from the python side. You will need to initialize with a title object. This works for me in the fiddle:

 title: new Bokeh.Title({text:"A test line plot"}),

including an update in a callback with p.title.text = ...

As this is really a usage question I ask that any further discussion happen on the discourse, and not here on the tracker.