Customizing JupyterLab using extensions

JupyterLab is the next generation UI for Project Jupyter and intended to replace the classic Jupyter Notebook UI. It is designed to be extendable and is itself a collection of extensions. The core extensions of JupyterLab are purposfully limited in scope with the expectation that developers will create extensions to customize their user’s experience. This demo walk-through is designed to show not only how to create and install a simple JupyterLab extension, but how to do so all within a running JupyterLab instance.

To start the walk-through, click on the Launch Binder link above to start JupyterLab. Then follow the instruction below.

Creating a lab extension

Once your binder instance of JupyterLab has started, follow the steps below to learn how you can create and install a lab extension all from within JupyterLab.

From the launcher tab, open a Terminal and run the following command to create a lab extension from a cookiecutter.
```
 cookiecutter https://github.com/jupyterlab/extension-cookiecutter-ts
```
Fill out the prompts (for our walkthrough, the values do not matter) and then open the newly created directory in the file browser on the left. (Note: you may need to click the refresh icon for the new directory to display.)
In our newly created extension directory, we will want to make some simple code changes. By default, the new extension will only log to the browser console and we want it to do a little more than that.
1. Edit package.json (to edit rather than view json files, right-click the file and select Open With > Editor) then add the following to the dependencies section:
```
 "@jupyterlab/apputils": "^2.0.0",
 "@jupyterlab/docregistry": "^2.0.0",
 "@jupyterlab/notebook": "^2.0.0",
 "@lumino/disposable":  "^1.3.5"
```
  You will need these for the imports in your .ts files.
2. Edit src/index.ts and add the following import:
```
 import {ButtonExtension} from "./button";
```
  then add the following to the activate function:
```
 let buttonExtension = new ButtonExtension();
 app.docRegistry.addWidgetExtension('Notebook', buttonExtension);
```
  This will import and create an example button extension, then add it to the registry so it will be available when editing notebooks.
3. Copy the button.ts file provided with this demo into the src directory. The file is located in the examples directory at the root of the file browser. To copy a file, just right-click on it and select Copy. To paste, either right-click the target directory, or if in the directory, right-click any whitespace in the file browser, and select Paste.
  
  Feel free to read through button.ts, each line of code has a short comment explaining its purpose.
Now we want to build our new extension. In the Terminal cd to your extension directory, then run the following to build and install your extension. The install steps are detailed further in the README for your extension.
```
 jlpm
 jlpm build
 jupyter labextension install .
```
Once the build finishes refresh your browser so JuyterLab can catch the rebuilt files. Now create a new Notebook from the Launcher and you’ll see your button in the toolbar, try clicking it.

Next Steps

Now that you’ve seen how easy it is to create a simple extension, try looking at other extensions on GitHub for inspiration. Extensions can do a lot more than what you saw in the walk-through, including extending the JupyterLab API, creating your own editors and file viewers, or changing the UI theme. To help you get started I’ve included some helpful resources below, including an older video presentation that this walk-through was based off of.

SciPy2020

Customizing JupyterLab using extensions

Creating a lab extension

Next Steps

Resources