F11 keyboard shortcut triggers unregistered `application:toggle-fullscreen-mode` command on the `/tree` page

[visheshbpatel]

Description

Pressing F11 on the /tree page does not enter fullscreen mode. Instead, the browser console reports that the associated command is not registered.

Once a notebook (.ipynb) or another file is opened, pressing F11 works as expected.

While investigating this issue, I found that the command application:toggle-fullscreen-mode is defined and registered in the JupyterLab repository, but I could not find an equivalent definition or registration in the Jupyter Notebook repository.

I'm reporting the observed behavior together with the investigation in case this is a regression or an integration issue.

---

Reproduce

1. Clone the Jupyter Notebook repository.
2. Follow the development setup instructions in CONTRIBUTING.md.
3. Build and run Jupyter Notebook from the current main branch.
4. Open the /tree page (http://localhost:8888/tree).
5. Press F11.

Actual Behavior

Nothing happens.

The browser console reports:

Cannot execute key binding 'F11':
command 'application:toggle-fullscreen-mode'
is not registered.

Additional Observation

• Opening a notebook (.ipynb) or another file and pressing F11 works as expected.
• The issue appears to be specific to the /tree page.
• Screenshots of both the /tree page (where the issue occurs) and the notebook view (where F11 works as expected) are attached below.

---

Investigation

During the investigation, I observed the following:

• The browser console consistently reports:

  Cannot execute key binding 'F11':
  command 'application:toggle-fullscreen-mode'
  is not registered.
  

• Searching the Jupyter Notebook repository did not find a definition or registration for application:toggle-fullscreen-mode.
• The JupyterLab repository defines and registers application:toggle-fullscreen-mode.
• I searched the Notebook repository history using:

git log -S "application:toggle-fullscreen-mode" --all

but did not find any previous definition of this command.

Based on this investigation, it appears that the /tree page attempts to invoke application:toggle-fullscreen-mode, but that command does not appear to be registered there.

---

Expected behavior

Pressing F11 on the /tree page should either:

• execute the configured fullscreen action, or
• not reference an unregistered command.

Its behavior should be consistent with the notebook view.

---

Context

• Operating System: Windows 11
• Browser: Google Chrome
• Python: 3.14.0
• Jupyter Notebook version: 7.7.0a0 (built from the current main branch)

---

Troubleshoot Output

sys.executable:
    V:\OpenSource\notebook\.venv\Scripts\python.exe

sys.version:
    3.14.0

platform.platform():
    Windows-11-10.0.26200-SP0

where jupyter:
    V:\OpenSource\notebook\.venv\Scripts\jupyter.exe
    C:\Users\Asus\AppData\Local\Programs\Python\Python314\Scripts\jupyter.exe

Notebook version:
    7.7.0a0 (editable installation from local source)

(The complete `jupyter troubleshoot` output can be provided if needed.)

---

Command Line Output

[I ...] notebook | extension was successfully linked.
[I ...] notebook | extension was successfully loaded.
[I ...] Serving notebooks from local directory:
         V:\OpenSource\notebook

http://localhost:8888/tree

---

Browser Output

Cannot execute key binding 'F11':
command 'application:toggle-fullscreen-mode'
is not registered.

---

[KabiththananParan]

Hi! I'd like to work on this issue if it's not already being handled by someone else. I'll investigate the root cause first and, if I identify a suitable fix, I'll open a pull request. Please let me know if there are any specific considerations I should keep in mind.

[visheshbpatel]

Thanks for your interest!

I opened this issue after investigating the behavior, reproducing it locally, and narrowing it down to the /tree page, where F11 triggers an unregistered application:toggle-fullscreen-mode command.

I'd also like to work on a fix for this as a learning opportunity, if the maintainers think that's appropriate. Happy to follow the project's preferred workflow.

[andrii-i]

@visheshbpatel @KabiththananParan thank you for creating or commenting on this issue. If you would have an opportunity to test this in JupyterLab, please do and comment back here on the results, this would be highly appreciated.

Thank you.

[visheshbpatel]

Hi @andrii-i,

I tested this in JupyterLab and could not reproduce the issue. Pressing F11 works as expected there, and the fullscreen command is available.

The issue appears to be specific to Jupyter Notebook (tested on 7.7.0a0). On the /tree page, pressing F11 consistently results in:

Cannot execute key binding 'F11':
command 'application:toggle-fullscreen-mode'
is not registered.

I'm currently investigating the Notebook implementation to identify the root cause. I'll update this issue once I have a clear understanding of what's causing the problem.