Textarea.scroll_to_bottom alternative

[mouad-ouali]

I've been working on some code that used Textarea's scroll_to_bottom method. Basically, there is a textarea widget that works as a logging handler in a jupyter notebook, and everytime there is a new log message, it should scroll to the bottom to only show the latest log messages.

After updating to 7.0 , I learned that Textarea.scroll_to_bottom was removed and that it hasn't been working for a while anyway.

I've been looking for a way to make the textarea scroll to bottom by sending messages from the backend, but I can't figure out the proper way to do it. I'm not even sure it's possible using messages because the examples of custom messages I found simply called a function from the frontend, and in the case of Textarea, that function no longer exists.

I also tried looking at the model attributes of Textarea but it seems that only a few frontend attributes are exposed, therefore I cannot do something like this.$textbox.scrollTop(this.$textbox[0].scrollHeight); in Python.

Is there a different approach I could've taken to achieve the scroll to bottom behavior, and if possible, a way that works on both 7.0 and 6.0?

[jasongrout]

As you saw, scroll to bottom method was removed after it wasn't working for a while.

Let's see if we can find a better solution for your use case. For example, one issue with a scroll to bottom function blindly applied on new output is that if I've scrolled up to look at a record, new output jumps my scroll to the bottom, interrupting my reading.

One thought is to prepend to the top instead of the bottom (reverse sort the log), but that likely suffers from the same problem as above.

It's probably best to make a log-viewing widget that would either pin to the bottom if you're already scrolled at the bottom, or don't scroll to the bottom if it is scrolled anywhere else.

[jasongrout]

(I would suggest such a widget could be experimented with as a third-party widget, using something like https://github.com/vidartf/opinionated-widget-cookiecutter)

[RDeRenzi]

It's probably best to make a log-viewing widget that would either pin to the bottom if you're already scrolled at the bottom, or don't scroll to the bottom if it is scrolled anywhere else.

I also find this is the correct behaviour. And I miss it in my TextArea applications.

[deeplook]

I was about to open a new issue when I found this one. Seems like there is no solution, right? My description would have been the following:

What is the recommended way to achieve the the effect of having a textarea widget's content automatically scroll up, when its content becomes too large to fit in it entirely and it will show a scrollbar? I was trying to use Layout(overflow_y='scroll'), but that seems to have no effect, and the documentation is pretty sparse on any overflow attributes. But then, I'm not sure this is the right attribute to think of, anyway.

[RDeRenzi]

I am coming back to this issue. When using Output as logging widget the optimal would be that described by jasongrout, indeed the xterm behavior. Upon a new addition to Output

• do not jump if scrolling is not positioned at the bottom,
• jump to the bottom if the present position is already at the bottom or the existing text.

If ipywidget Output still cannot be instructed to behave like this (can it?), my alternative is to use the an external xterm (unfortunately this workaround is only for linux)

        import os
        import platform 
        from shutil import which
        from subprocess import Popen`       
        if platform.system()=='Linux':
            if which('gnome-terminal') is not None:
                pipe = "/tmp/my_pipe"
                if not os.path.exists(self._output_):
                    os.mkfifo(self._output_)
                terminal = 'gnome-terminal' # or more safely xterm
                Popen([terminal,'shell=False',settitle,'-e', 'tail -f %s' % pipe])
                sting = 'output text example'
  `             p = open(pipe,'w')  # the following three llines can be repeated n times
                p.write(''.join([string,'\n']))
                p.close()

[SvenSchiffner]

I stumbled over this issue today and didn't found any solution. I added a max_height to an Output widget and want to automatically scroll to the bottom.
I found a possible CSS-only solution. And a first test in firefox looks very promising. But the whole CSS and Javascript stuff is a secret for me and it would take me a lot of time so get into it. Otherwise I would provide a pull request. Maybe someone can create it with this hint or give me some advice how I can modify the Output widget.

Thank you very much!