Explaining selectionStart in Dash Input component

Dash Python
1

I’ve been trying to use selectionStart inside the dcc.Input() but I’m not sure how to make it work according to the documentation. This is my code so far:

app.layout = html.Div([
    html.Div([
        dcc.Input(
            id='my_txt_input',
            type='text',
            debounce=True,
            #selectionStart=" ",
        ),
    ]),

    html.Div(id='div_output'),

    html.P(['Selection Start:']),
    html.Div(id='div_slct_Start'),

])

@app.callback(
    [Output(component_id='div_output', component_property='children'),
     Output(component_id='div_slct_Start', component_property='children')
    ],
    [Input(component_id='my_txt_input', component_property='value'),
     Input(component_id="my_txt_input", component_property='selectionStart')
    ]
)

def update_input(txt_inserted, slct_start)
    return(txt_inserted, slct_start)

Nothing seems to happen, and I always get a None type. This example demonstrates how selectionStart is read.

Can someone please explain how selectionStart works inside dcc.Input()
Thank you,

2

Is there any update on this? I have been trying to get cursor position in input field so I could insert text on that position and I came across selectionStart and selectionEnd properties, but they do not seem to work. I also always get a None type when using them with n_submit or n_blur properties of Input for callback

3

Decided to start a New Topic since this is a 2-parter and since this thread has been dormant for over a year.

Moving to New Topic:

Me too.

Supplying selectionStart (or -End) as a callback Input or State only ever gives me the initial value (provided I had set one explicitly in the layout). My code is essentially identical to adamschroeder’s (above).

Also, I ultimately will need to use this functionality in a Textarea also, but I only see this property associated with Input. That seems like an odd asymmetry. It’s arguably even more useful in a Textarea where people might be expected to do more complex editing etc - you know, as I am literally doing as I type this. :wink: In fact, my goal is to put some Markdown buttons on my Inputs and Textareas not unlike what is on this very widget.

Thanks a bunch!
John