Extension Migration Guide

JupyterLab 3.5 to 3.6

AsyncIterable Support

For the events service, we are using a JavaScript feature introduced in ES2018. If your code is using TypeScript with ES2017 target (as JupyterLab 3.6), you will either need to update your target to ES2018 or add "ES2018" to the TypeScript lib option.


JupyterLab 3.6.0 was released with an updated target “ES2018”. We strongly advise updating to 3.6.1, which reverts the target back to “ES2017”.

Jest configuration update

If you are using jest to test your extension, some new ES6 packages dependencies are added to JupyterLab 3.6. They need to be ignore when transforming the code with Jest. You will need to update the transformIgnorePatterns to match:

const esModules = [

// ...

transformIgnorePatterns: [`/node_modules/(?!${esModules}).+`]

For more information, have a look at Testing your extension.

Real-Time Collaboration

In JupyterLab v3.6, it is necessary to install Jupyter Server v2.0 to use real-time collaboration. This requirement was introduced to take advantage of the new identity API in Jupyter Server v2.0.

On the other side, we also changed how JupyterLab loads documents (only in collaborative mode). Instead of using the content API, now the provider opens a WebSocket connection to the YDocWebSocketHandler, which is implemented in an external jupyter server extension.

In addition, the shared models’ package was moved to an external package called @jupyter/ydoc. @jupyterlab/shared-models has been kept for backward compatibility (except in 3.6.0 and 3.6.1). It is now a proxy to @jupyter/ydoc@~0.2.2; the API is almost the same; see the required modification for the example.

API Changes:

To be able to fix RTC and make it stable. It was necessary to change the API and make a few breaking changes. These changes should not affect the vast majority of extensions. They will only affect a couple of extensions focused on RTC.

It was necessary to change the paradigm of how JupyterLab loads documents and replace the locking mechanism in the back-end. Instead of identifying the first client to open the document, it now centralizes the process by instantiating a YDoc client in the back-end. This client is the only one that loads the content of the document into memory and shares it with every other client connected.

The involved packages are:

  • @jupyterlab/docprovider:
    • The interface IDocumentProvider, now extends from IDisposable. Removed: acquireLock, releaseLock, setPath, destroy, requestInitialContent and putInitializedState. Added: ready and isDisposed.

    • IDocumentProviderFactory.IOptions is now templated with T extends ISharedDocument = ISharedDocument. And the ymodel attribute has been renamed model typed T (relaxing typing from YDocument to ISharedDocument).

    • WebSocketProviderWithLocks has been renamed to WebSocketProvider. It does not extend WebSocketProvider from y-websocket anymore.

    • WebSocketProvider.IOptions has a new optional attribute, user.

  • @jupyterlab/shared-models: It is now a proxy to @jupyter/ydoc@~0.2.2.
    • A document model extending YDocument must define a change interface extending DocumentChange.

  • @jupyterlab/services:
    • The interface IManager has a new optional property, user that implement User.IManager.

    • The ServiceManager class implements the optional property user from the IManager.

Future changes: Some of the behavior changes coming in JupyterLab 4.0 were made available behind a flag in JupyterLab 3.6:

  • In JupyterLab 3.x, the CSS for a _disabled_ prebuilt extensions is always loaded on the page. This will no longer be the case in JupyterLab 4.0. To preview the impact of these changes on your extension/theme start JupyterLab with --future-skip-styles-for-disabled flag.

JupyterLab 3.0 to 3.1

Following semver rules, API are compatible.

New main and context menus customization

JupyterLab 3.1 introduces a new way to hook commands into Main Menu and Context Menu. It allows the final user to customize those menus through settings as it is already possible for the shortcuts.

Jest configuration update

If you are using jest to test your extension, some new ES6 packages dependencies are added to JupyterLab. They need to be ignore when transforming the code with Jest. You will need to update the transformIgnorePatterns to match:

const esModules = [

// ...

transformIgnorePatterns: [`/node_modules/(?!${esModules}).+`]

For more information, have a look at Testing your extension.


Here is an example of pull request to update to JupyterLab 3.1 in @jupyterlab/git extension: https://github.com/jupyterlab/jupyterlab-git/pull/979/files

JupyterLab 2.x to 3.x

Here are some helpful tips for migrating an extension from JupyterLab 2.x to JupyterLab 3.x.

Upgrading library versions manually

To update the extensions so it is compatible with the 3.0 release, update the compatibility range of the @jupyterlab dependencies in the package.json. The diff should be similar to:

index 6f1562f..3fcdf37 100644
^^^ a/package.json
+++ b/package.json
   "dependencies": {
-    "@jupyterlab/application": "^2.0.0",
+    "@jupyterlab/application": "^3.0.0",

Upgrading library versions using the upgrade script

JupyterLab 3.0 provides a script to upgrade an existing extension to use the new extension system and packaging.

First, make sure to update to JupyterLab 3.0 and install jupyter-packaging and cookiecutter. With pip:

pip install jupyterlab -U
pip install jupyter-packaging cookiecutter

Or with conda:

conda install -c conda-forge jupyterlab=3 jupyter-packaging cookiecutter

Then at the root folder of the extension, run:

python -m jupyterlab.upgrade_extension .

The upgrade script creates the necessary files for packaging the JupyterLab extension as a Python package, such as setup.py and pyproject.toml.

The upgrade script also updates the dependencies in package.json to the ^3.0.0 packages. Here is an example diff:

index 6f1562f..3fcdf37 100644
^^^ a/package.json
+++ b/package.json
@@ -29,9 +29,13 @@
   "scripts": {
-    "build": "tsc",
-    "build:labextension": "npm run clean:labextension && mkdirp myextension/labextension && cd myextension/labextension && npm pack ../..",
-    "clean": "rimraf lib tsconfig.tsbuildinfo",
+    "build": "jlpm run build:lib && jlpm run build:labextension:dev",
+    "build:prod": "jlpm run build:lib && jlpm run build:labextension",
+    "build:lib": "tsc",
+    "build:labextension": "jupyter labextension build .",
+    "build:labextension:dev": "jupyter labextension build --development True .",
+    "clean": "rimraf lib tsconfig.tsbuildinfo myextension/labextension",
+    "clean:all": "jlpm run clean:lib && jlpm run clean:labextension",
   "clean:labextension": "rimraf myextension/labextension",
   "eslint": "eslint . --ext .ts,.tsx --fix",
   "eslint:check": "eslint . --ext .ts,.tsx",
@@ -59,12 +63,12 @@
   "dependencies": {
-    "@jupyterlab/application": "^2.0.0",
-    "@jupyterlab/apputils": "^2.0.0",
-    "@jupyterlab/observables": "^3.0.0",
+    "@jupyterlab/builder": "^3.0.0",
+    "@jupyterlab/application": "^3.0.0",
+    "@jupyterlab/apputils": "^3.0.0",
+    "@jupyterlab/observables": "^3.0.0",
   "@lumino/algorithm": "^1.2.3",
   "@lumino/commands": "^1.10.1",
   "@lumino/disposable": "^1.3.5",
@@ -99,6 +103,13 @@
-    "typescript": "~3.8.3"
+    "typescript": "~4.0.1"
   "jupyterlab": {
-    "extension": "lib/plugin"
+    "extension": "lib/plugin",
+    "outputDir": "myextension/labextension/"

On the diff above, we see that additional development scripts are also added, as they are used by the new extension system workflow.

The diff also shows the new @jupyterlab/builder as a devDependency. @jupyterlab/builder is a package required to build the extension as a federated (prebuilt) extension. It hides away internal dependencies such as webpack, and produces the assets that can then be distributed as part of a Python package.

Extension developers do not need to interact with @jupyterlab/builder directly, but instead can use the jupyter labextension build command. This command is run automatically as part of the build script (jlpm run build).

For more details about the new file structure and packaging of the extension, check out the extension tutorial: Extension Tutorial

Publishing the extension to PyPI and conda-forge

Starting from JupyterLab 3.0, extensions can be distributed as a Python package.

The extension tutorial provides explanations to package the extension so it can be published on PyPI and conda forge: Publishing your extension.


While publishing to PyPI is the new recommended way for distributing extensions to users, it is still useful to continue publishing extensions to npm as well, so other developers can extend them in their own extensions.

JupyterLab 1.x to 2.x

Here are some helpful tips for migrating an extension from JupyterLab 1.x to JupyterLab 2.x. We will look at two examples of extensions that cover most of the APIs that extension authors might be using:

Upgrading library versions

The @phosphor/* libraries that JupyterLab 1.x uses have been renamed to @lumino/*. Updating your package.json is straightforward. The easiest way to do this is to look in the JupyterLab core packages code base and to simply adopt the versions of the relevant libraries that are used there.

Updating the debugger extension’s libraries in package.json

Updating the shortcuts UI extension’s libraries in package.json


In these examples, note that we are using the 2.0.0-beta.x version of many libraries. This was to test the extensions against the JupyterLab 2.0 beta release before the final version. For the final release, your package.json should depend on version ^2.0.0 of these packages.

Migrating from @phosphor to @lumino ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-

The foundational packages used by JupyterLab are now all prefixed with the NPM namespace @lumino instead of @phosphor. The APIs for these packages have not changed. The @phosphor namespaced imports need to be updated to the new @lumino namespaced packages:

Update from @phosphor/... to @lumino/...


































p- prefixed CSS classes, data-p- attributes and p- DOM events are deprecated. They will continue to work until the next major release of Lumino.

  • .p- CSS classes such as .p-Widget should be updated to .lm-, e.g. .lm-Widget

  • data-p- attributes such as data-p-dragscroll should be updated to data-lm-, e.g. data-lm-dragscroll

  • p- DOM events such as p-dragenter should be updated to lm-, e.g. lm-dragenter

Updating former @jupyterlab/coreutils imports ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-

JupyterLab 2.0 introduces several new packages with classes and tokens that have been moved out of @jupyterlab/coreutils into their own packages. These exports have been moved.


It might be helpful to delete node_modules and yarn.lock when updating these libraries.











































Using Session and SessionContext to manage kernel sessions


For full API documentation and examples of how to use @jupyterlab/services, consult the repository.

ConsolePanel and NotebookPanel now expose a sessionContext: ISessionContext attribute that allows for a uniform way to interact with kernel sessions.

Any widget that matches the interface IDocumentWidget has a context: DocumentRegistry.IContext attribute with a sessionContext: ISessionContext attribute.

For example, consider how the @jupyterlab/debugger extension’s DebuggerService updated its isAvailable() method.

From the PR migrating the debugger extension to JupyterLab 2.0


await kernel.ready is no longer necessary before the kernel connection kernel can be used. Kernel messages will be buffered as needed while a kernel connection is coming online, so you should be able to use a kernel connection immediately. If you want to retrieve the kernel info (or if for some other reason you want to wait until at least one message has returned from a new kernel connection), you can do await kernel.info.

Using the new icon system and LabIcon


For full API documentation and examples of how to use the new icon support based on LabIcon from @jupyterlab/ui-components, consult the repository.