launcher

Launcher

Start your extension from the Launcher.

In this example, you will learn how to start your extension from the launcher and how to have optional dependencies to JupyterLab features.

Credit: This example is copied from Jeremy Tuloup Python file extension.

This example allows to create an empty Python file. To do so, your extension will use two commands defined by the documents manager of JupyterLab:

• 'docmanager:new-untitled': Create new untitled document
• 'docmanager:open': Open a document

The command will create a new Python file and then open it:

// src/index.ts#L44-L66

commands.addCommand(command, {
  label: args => (args['isPalette'] ? 'New Python File' : 'Python File'),
  caption: 'Create a new Python file',
  icon: args => (args['isPalette'] ? null : icon),
  execute: async args => {
    // Get the directory in which the Python file must be created;
    // otherwise take the current filebrowser directory
    const cwd = args['cwd'] || browserFactory.defaultBrowser.model.path;

    // Create a new untitled python file
    const model = await commands.execute('docmanager:new-untitled', {
      path: cwd,
      type: 'file',
      ext: 'py'
    });

    // Open the newly created file with the 'Editor'
    return commands.execute('docmanager:open', {
      path: model.path,
      factory: FACTORY
    });
  }
});

To link that command to the JupyterLab launcher, the ILauncher interface needs to be passed to the activate extension function. As that interface is provided by the @jupyterlab/launcher package, it needs first to be installed:

jlpm add @jupyterlab/launcher

Then you can use it in the extension by importing it:

// src/index.ts#L10-L10

import { ILauncher } from '@jupyterlab/launcher';

And finally you can add it to the list of dependencies:

// src/index.ts#L25-L36

const extension: JupyterFrontEndPlugin<void> = {
  id: 'launcher',
  autoStart: true,
  requires: [IFileBrowserFactory],
  optional: [ILauncher, IMainMenu, ICommandPalette],
  activate: (
    app: JupyterFrontEnd,
    browserFactory: IFileBrowserFactory,
    launcher: ILauncher | null,
    menu: IMainMenu | null,
    palette: ICommandPalette | null
  ) => {

In this example, the ILauncher interface is requested as optional dependency and not as a required dependency. This lets other applications without a launcher be able to use your extension.

If the application is unable to provide an optional interface, it will take a null value.

Therefore before adding the command to the launcher, you need to check if the launcher variable is not null:

// src/index.ts#L68-L75

// Add the command to the launcher
if (launcher) {
  launcher.add({
    command,
    category: 'Extension Examples',
    rank: 1
  });
}

Where to Go Next

This example uses a command. This is an essential concept of JupyterLab. To know more about it have a look at the command example.

An user can execute a command from other UI elements than the launcher. To know more about those other possibilities, you could look at the following examples:

• Add the command to the command palette
• Add the command to a menu