jupyterlab-markdown-switch-tab-scrolling-fix 1.0.5

Jupyterlab bugfix (disguised as extension) to help with the problem of Markdown files getting scrolled uncontrollably when images are gettng loaded into the view when switching tab back and forth

jupyterlab_markdown_switch_tab_scrolling_fix

JupyterLab extension that prevents markdown files from scrolling uncontrollably when switching tabs while images load.

[!WARNING] This extension is a temporary fix and will be deprecated once JupyterLab core implements proper icon scaling. We plan to submit a PR to the main JupyterLab repository to address this issue natively. Once accepted and released, this extension will no longer be necessary.

The Problem

When you switch back to a markdown tab in JupyterLab, images reload and cause the viewport to jump as they render. This creates disorienting scroll drift that moves you away from where you were reading.

Key observations:

• Issue only occurs with markdown files containing images
• Triggered by tab switching (deactivate then reactivate)
• Browser recalculates layout as each image loads, causing cumulative scroll displacement
• Native JupyterLab has no scroll position protection during image rendering

The Fix

This extension locks scroll position when you switch to a markdown tab until all images finish loading.

How it works:

• Detects when markdown widgets become active via JupyterLab's shell signals
• Captures initial scroll position immediately on tab activation
• Monitors all image load events in the markdown
• Actively corrects any scroll drift (checks every 100ms)
• Releases lock after all images load and position stabilizes for 300ms
• User scroll (wheel or touch) immediately overrides the lock

Implementation details:

• Maximum lock duration: 3 seconds
• Handles cached images that load instantly
• Uses WeakMap to prevent multiple guards on same widget
• Passive event listeners for performance

Technical Implementation

The extension hooks into JupyterLab's shell lifecycle using the ILabShell.currentChanged signal to detect tab switches. When a markdown widget activates, the handler searches for .jp-RenderedMarkdown containers and queries all image elements. It captures the initial scroll position (scrollTop/scrollLeft), then attaches load event listeners to track completion of image rendering.

A guard interval runs every 100ms, comparing current scroll position against the saved position. Any drift exceeding 1 pixel triggers immediate correction by resetting scrollTop/scrollLeft. The guard tracks stability (position unchanged for 300ms) and image load completion. Once all images finish loading and position remains stable, the guard releases. User scroll events (wheel or touchstart) immediately abort the guard to preserve manual navigation.

Core components:

• ILabShell.currentChanged signal handler detects widget activation
• DOM query selects .jp-RenderedMarkdown img elements for monitoring
• addEventListener('load', handler, { once: true }) tracks image completion
• window.setInterval() guard runs drift correction every 100ms
• WeakMap associates guard interval IDs with widget instances
• Passive event listeners detect user scroll intent without blocking

Requirements

• JupyterLab >= 4.0.0

Install

To install the extension, execute:

pip install jupyterlab_markdown_switch_tab_scrolling_fix

Uninstall

To remove the extension, execute:

pip uninstall jupyterlab_markdown_switch_tab_scrolling_fix

Contributing

Development install

Note: You will need NodeJS to build the extension package.

The jlpm command is JupyterLab's pinned version of yarn that is installed with JupyterLab. You may use yarn or npm in lieu of jlpm below.

# Clone the repo to your local environment
# Change directory to the jupyterlab_markdown_switch_tab_scrolling_fix directory

# Set up a virtual environment and install package in development mode
python -m venv .venv
source .venv/bin/activate
pip install --editable "."

# Link your development version of the extension with JupyterLab
jupyter labextension develop . --overwrite

# Rebuild extension Typescript source after making changes
# IMPORTANT: Unlike the steps above which are performed only once, do this step
# every time you make a change.
jlpm build

You can watch the source directory and run JupyterLab at the same time in different terminals to watch for changes in the extension's source and automatically rebuild the extension.

# Watch the source directory in one terminal, automatically rebuilding when needed
jlpm watch
# Run JupyterLab in another terminal
jupyter lab

With the watch command running, every saved change will immediately be built locally and available in your running JupyterLab. Refresh JupyterLab to load the change in your browser (you may need to wait several seconds for the extension to be rebuilt).

By default, the jlpm build command generates the source maps for this extension to make it easier to debug using the browser dev tools. To also generate source maps for the JupyterLab core extensions, you can run the following command:

jupyter lab build --minimize=False

Development uninstall

pip uninstall jupyterlab_markdown_switch_tab_scrolling_fix

In development mode, you will also need to remove the symlink created by jupyter labextension develop command. To find its location, you can run jupyter labextension list to figure out where the labextensions folder is located. Then you can remove the symlink named jupyterlab_markdown_switch_tab_scrolling_fix within that folder.

Testing the extension

Frontend tests

This extension is using Jest for JavaScript code testing.

To execute them, execute:

jlpm
jlpm test

Integration tests

This extension uses Playwright for the integration tests (aka user level tests). More precisely, the JupyterLab helper Galata is used to handle testing the extension in JupyterLab.

More information are provided within the ui-tests README.

Packaging the extension

See RELEASE