Create a jupyter_server extension for the classic notebook.

[SylvainCorlay]

This could be in a classic_notebook repository on the jupyter organization, or as a PR on the actual classic notebook (with a greater risk of not being merged).

The classic_notebook extension could be a way to enable the classic notebook button with JupyterLab when it is installed on the top of the jupyter_server.

[SylvainCorlay]

Following some discussions with @minrk on this. There are two main ways to go with this

1. Create a new classic_notebook project which either depends on notebook and allows the jupyter server to server the classic notebook JavaScript.
2. Open a PR to the notebook repository to make it use the Jupyter server.

The second approach would be more disruptive for the classic notebook repository which is presumably under maintenance mode, but would result in less duplication. Also, it would mean that the classic notebook would need to be updated upon backward incompatible changes in jupyter_server... An advantage though would be that PRs improving the current notebook server would apply to jupyter_server and won't fall between the cracks.

cc @takluyver @gnestor.

[blink1073]

👍 for the second approach, I think it is easier to explain to users as well.

[gnestor]

I think second approach sounds better too

[Zsailer]

Here's my experiment—making the classic notebook a jupyter_server extension (using the API from #48). It's so much cleaner!

https://github.com/Zsailer/notebook_server_extension

@SylvainCorlay — Should I open a the dracarys PR in notebook? 😉

[Zsailer]

See this PR in the classic notebook.

[Zsailer]

Closing for now, since NBClassic exists.