Common Extension Points

Most of the component parts of JupyterLab are designed to be extensible, and they provide services that can be requested in extensions via tokens. A list of common core tokens that extension authors can request is given in Core Tokens.

Following the list of core tokens is a guide for using some of JupyterLab’s most commonly-used extension points. However, it is not an exhaustive account of how to extend the application components, and more detailed descriptions of their public APIs may be found in the JupyterLab and Lumino API documentation.

Core Tokens

The core packages of JupyterLab provide many services for plugins. The tokens for these services are listed here, along with short descriptions of when you might want to use the services in your extensions.

• @jupyterlab/application:IConnectionLost: A service for invoking the dialog shown when JupyterLab has lost its connection to the server. Use this if, for some reason, you want to bring up the “connection lost” dialog under new circumstances.

• @jupyterlab/application:IInfo: A service providing metadata about the current application, including disabled extensions and whether dev mode is enabled.

• @jupyterlab/application:IPaths: A service providing information about various URLs and server paths for the current application. Use this service if you want to assemble URLs to use the JupyterLab REST API.

• @jupyterlab/application:ILabStatus: A service for interacting with the application busy/dirty status. Use this if you want to set the application “busy” favicon, or to set the application “dirty” status, which asks the user for confirmation before leaving the application page.

• @jupyterlab/application:ILabShell: A service for interacting with the JupyterLab shell. The top-level application object also has a reference to the shell, but it has a restricted interface in order to be agnostic to different shell implementations on the application. Use this to get more detailed information about currently active widgets and layout state.

• @jupyterlab/application:ILayoutRestorer: A service providing application layout restoration functionality. Use this to have your activities restored across page loads.

• @jupyterlab/application:IMimeDocumentTracker: A widget tracker for documents rendered using a mime renderer extension. Use this if you want to list and interact with documents rendered by such extensions.

• @jupyterlab/application:IRouter: The URL router used by the application. Use this to add custom URL-routing for your extension (e.g., to invoke a command if the user navigates to a sub-path).

• @jupyterlab/apputils:ICommandPalette: A service for the application command palette in the left panel. Use this to add commands to the palette.

• @jupyterlab/apputils:ISplashScreen: A service for the splash screen for the application. Use this if you want to show the splash screen for your own purposes.

• @jupyterlab/apputils:IThemeManager: A service for the theme manager for the application. This is used primarily in theme extensions to register new themes.

• @jupyterlab/apputils:IToolbarWidgetRegistry: A registry for toolbar widgets. Require this if you want to build the toolbar dynamically from a data definition (stored in settings for example).

• @jupyterlab/apputils:IWindowResolver: A service for a window resolver for the application. JupyterLab workspaces are given a name, which are determined using the window resolver. Require this if you want to use the name of the current workspace.

• @jupyterlab/codeeditor:IEditorServices: A service for the text editor provider for the application. Use this to create new text editors and host them in your UI elements.

• @jupyterlab/completer:ICompletionManager: A service for the completion manager for the application. Use this to allow your extension to invoke a completer.

• @jupyterlab/console:IConsoleTracker: A widget tracker for code consoles. Use this if you want to be able to iterate over and interact with code consoles created by the application.

• @jupyterlab/console:IContentFactory: A factory object that creates new code consoles. Use this if you want to create and host code consoles in your own UI elements.

• @jupyterlab/docmanager:IDocumentManager: A service for the manager for all documents used by the application. Use this if you want to open and close documents, create and delete files, and otherwise interact with the file system.

• @jupyterlab/docprovider:IDocumentProviderFactory: A factory object that creates new providers for shared documents. Use this if you want to create a provider for a new shared document.

• @jupyterlab/documentsearch:ISearchProviderRegistry: A service for a registry of search providers for the application. Plugins can register their UI elements with this registry to provide find/replace support.

• @jupyterlab/filebrowser:IFileBrowserFactory: A factory object that creates file browsers. Use this if you want to create your own file browser (e.g., for a custom storage backend), or to interact with other file browsers that have been created by extensions.

• @jupyterlab/fileeditor:IEditorTracker: A widget tracker for file editors. Use this if you want to be able to iterate over and interact with file editors created by the application.

• @jupyterlab/htmlviewer:IHTMLViewerTracker: A widget tracker for rendered HTML documents. Use this if you want to be able to iterate over and interact with HTML documents viewed by the application.

• @jupyterlab/imageviewer:IImageTracker: A widget tracker for images. Use this if you want to be able to iterate over and interact with images viewed by the application.

• @jupyterlab/inspector:IInspector: A service for adding contextual help to widgets (visible using “Show Contextual Help” from the Help menu). Use this to hook into the contextual help system in your extension.

• @jupyterlab/launcher:ILauncher: A service for the application activity launcher. Use this to add your extension activities to the launcher panel.

• @jupyterlab/mainmenu:IMainMenu: A service for the main menu bar for the application. Use this if you want to add your own menu items or provide implementations for standardized menu items for specific activities.

• @jupyterlab/markdownviewer:IMarkdownViewerTracker: A widget tracker for markdown document viewers. Use this if you want to iterate over and interact with rendered markdown documents.

• @jupyterlab/notebook:INotebookTools: A service for the Notebook Tools panel in the right sidebar. Use this to add your own functionality to the panel.

• @jupyterlab/notebook:IContentFactory: A factory object that creates new notebooks. Use this if you want to create and host notebooks in your own UI elements.

• @jupyterlab/notebook:INotebookTracker: A widget tracker for notebooks. Use this if you want to be able to iterate over and interact with notebooks created by the application.

• @jupyterlab/rendermime:IRenderMimeRegistry: A service for the rendermime registry for the application. Use this to create renderers for various mime-types in your extension. Many times it will be easier to create a mime renderer extension rather than using this service directly.

• @jupyterlab/rendermime:ILatexTypesetter: A service for the LaTeX typesetter for the application. Use this if you want to typeset math in your extension.

• @jupyterlab/settingeditor:ISettingEditorTracker: A widget tracker for setting editors. Use this if you want to be able to iterate over and interact with setting editors created by the application.

• @jupyterlab/settingregistry:ISettingRegistry: A service for the JupyterLab settings system. Use this if you want to store settings for your application. See Plugin Settings for more information.

• @jupyterlab/statedb:IStateDB: A service for the JupyterLab state database. Use this if you want to store data that will persist across page loads. See state database for more information.

• @jupyterlab/statusbar:IStatusBar: A service for the status bar on the application. Use this if you want to add new status bar items.

• @jupyterlab/terminal:ITerminalTracker: A widget tracker for terminals. Use this if you want to be able to iterate over and interact with terminals created by the application.

• @jupyterlab/tooltip:ITooltipManager: A service for the tooltip manager for the application. Use this to allow your extension to invoke a tooltip.

• @jupyterlab/vdom:IVDOMTracker: A widget tracker for virtual DOM (VDOM) documents. Use this to iterate over and interact with VDOM document instances created by the application.

Commands

Add a Command to the Command Registry

Perhaps the most common way to add functionality to JupyterLab is via commands. These are lightweight objects that include a function to execute combined with additional metadata, including how they are labeled and when they are to be enabled. The application has a single command registry, keyed by string command IDs, to which you can add your custom commands.

The commands added to the command registry can then be used to populate several of the JupyterLab user interface elements, including menus and the launcher.

Here is a sample block of code that adds a command to the application (given by app):

const commandID = 'my-command';
let toggled = false;

app.commands.addCommand(commandID, {
  label: 'My Cool Command',
  isEnabled: () => true,
  isVisible: () => true,
  isToggled: () => toggled,
  iconClass: 'some-css-icon-class',
  execute: () => {
    console.log(`Executed ${commandID}`);
    toggled = !toggled;
});

This example adds a new command, which, when triggered, calls the execute function. isEnabled indicates whether the command is enabled, and determines whether renderings of it are greyed out. isToggled indicates whether to render a check mark next to the command. isVisible indicates whether to render the command at all. iconClass specifies a CSS class which can be used to display an icon next to renderings of the command.

Each of isEnabled, isToggled, and isVisible can be either a boolean value or a function that returns a boolean value, in case you want to do some logic in order to determine those conditions.

Likewise, each of label and iconClass can be either a string value or a function that returns a string value.

There are several more options which can be passed into the command registry when adding new commands. These are documented here.

After a command has been added to the application command registry you can add them to various places in the application user interface, where they will be rendered using the metadata you provided.

For example, you can add a button to the Notebook toolbar to run the command with the CommandToolbarButtonComponent.

Add a Command to the Command Palette

In order to add an existing, registered command to the command palette, you need to request the ICommandPalette token in your extension. Here is an example showing how to add a command to the command palette (given by palette):

palette.addItem({
  command: commandID,
  category: 'my-category',
  args: {}
});

The command ID is the same ID that you used when registering the command. You must also provide a category, which determines the subheading of the command palette in which to render the command. It can be a preexisting category (e.g., 'notebook'), or a new one of your own choosing.

The args are a JSON object that will be passed into your command’s functions at render/execute time. You can use these to customize the behavior of your command depending on how it is invoked. For instance, you can pass in args: { isPalette: true }. Your command label function can then check the args it is provided for isPalette, and return a different label in that case. This can be useful to make a single command flexible enough to work in multiple contexts.

Context Menu

JupyterLab has an application-wide context menu available as app.contextMenu. The application context menu is shown when the user right-clicks, and is populated with menu items that are most relevant to the thing that the user clicked.

The context menu system determines which items to show based on CSS selectors. It propagates up the DOM tree and tests whether a given HTML element matches the CSS selector provided by a given command.

Items can be added in the context menu in two ways:

1. Using the settings - this is the preferred way as they are configurable by the user.

2. Using the API - this is for advanced cases like dynamic menu or semantic items.

Here is an example showing how to add a command to the application context menu using the settings.

{
  "jupyter.lab.menus": {
  "context": [
    {
      "command": "my-command",
      "selector": ".jp-Notebook",
      "rank": 500
    }
  ]
}

In this example, the command with id my-command is shown whenever the user right-clicks on a DOM element matching .jp-Notebook (that is to say, a notebook). The selector can be any valid CSS selector, and may target your own UI elements, or existing ones. A list of CSS selectors currently used by context menu commands is given in Commonly used CSS selectors.

Item must follow this definition:

        "context": {
          "title": "The application context menu.",
          "description": "List of context menu items.",
          "items": {
            "allOf": [
              { "$ref": "#/definitions/menuItem" },
              {
                "properties": {
                  "selector": {
                    "description": "The CSS selector for the context menu item.",
                    "type": "string"
                  }
                }
              }
            ]
          },
          "type": "array",
          "default": []
        }

where menuItem definition is:

    "menuItem": {
      "properties": {
        "args": {
          "description": "Command arguments",
          "type": "object"
        },
        "command": {
          "description": "Command id",
          "type": "string"
        },
        "disabled": {
          "description": "Whether the item is disabled or not",
          "type": "boolean",
          "default": false
        },
        "type": {
          "description": "Item type",
          "type": "string",
          "enum": ["command", "submenu", "separator"],
          "default": "command"
        },
        "rank": {
          "description": "Item rank",
          "type": "number",
          "minimum": 0
        },
        "submenu": {
          "oneOf": [
            {
              "$ref": "#/definitions/menu"
            },
            {
              "type": "null"
            }
          ]
        }
      },
      "type": "object"
    },

The same example using the API is shown below. See the Lumino docs for the item creation options.

app.contextMenu.addItem({
  command: commandID,
  selector: '.jp-Notebook'
})

If you don’t want JupyterLab’s custom context menu to appear for your element, because you have your own right click behavior that you want to trigger, you can add the data-jp-suppress-context-menu data attribute to any node to have it and its children not trigger it.

For example, if you are building a custom React element, it would look like this:

function MyElement(props: {}) {
  return (
    <div data-jp-suppress-context-menu>
      <p>Hi</p>
      <p onContextMenu={() => {console.log("right clicked")}}>There</p>
    </div>
  )
}

Alternatively, you can use a ‘contextmenu’ event listener and call event.stopPropagation to prevent the application context menu handler from being called (it is listening in the bubble phase on the document). At this point you could show your own Lumino contextMenu, or simply stop propagation and let the system context menu be shown. This would look something like the following in a Widget subclass:

// In `onAfterAttach()`
this.node.addEventListener('contextmenu', this);

// In `handleEvent()`
case 'contextmenu':
  event.stopPropagation();

Copy Shareable Link

The file browser provides a context menu item “Copy Shareable Link”. The desired behavior will vary by deployment and the users it serves. The file browser supports overriding the behavior of this item.

import {
  IFileBrowserFactory
} from '@jupyterlab/filebrowser';

import {
  JupyterFrontEnd, JupyterFrontEndPlugin
} from '@jupyterlab/application';


const shareFile: JupyterFrontEndPlugin<void> = {
  activate: activateShareFile,
  id: commandID,
  requires: [IFileBrowserFactory],
  autoStart: true
};

function activateShareFile(
  app: JupyterFrontEnd,
  factory: IFileBrowserFactory
): void {
  const { commands } = app;
  const { tracker } = factory;

  commands.addCommand('filebrowser:share-main', {
    execute: () => {
      const widget = tracker.currentWidget;
      if (!widget) {
        return;
      }
      const path = encodeURI(widget.selectedItems().next().path);
      // Do something with path.
    },
    isVisible: () =>
      tracker.currentWidget &&
      toArray(tracker.currentWidget.selectedItems()).length === 1,
    iconClass: 'jp-MaterialIcon jp-LinkIcon',
    label: 'Copy Shareable Link'
  });
}

Note that an extension providing a replacement plugin like this must either automatically disable the replaced core plugin or the user must disable the core plugin manually:

jupyter labextension disable @jupyterlab/filebrowser-extension:share-file

Icons

See Reusing JupyterLab UI

Keyboard Shortcuts

There are two ways of adding keyboard shortcuts in JupyterLab. If you don’t want the shortcuts to be user-configurable, you can add them directly to the application command registry:

app.commands.addKeyBinding({
  command: commandID,
  args: {},
  keys: ['Accel T'],
  selector: '.jp-Notebook'
});

In this example my-command command is mapped to Accel T, where Accel corresponds to Cmd on a Mac and Ctrl on Windows and Linux computers.

The behavior for keyboard shortcuts is very similar to that of the context menu: the shortcut handler propagates up the DOM tree from the focused element and tests each element against the registered selectors. If a match is found, then that command is executed with the provided args. Full documentation for the options for addKeyBinding can be found here.

JupyterLab also provides integration with its settings system for keyboard shortcuts. Your extension can provide a settings schema with a jupyter.lab.shortcuts key, declaring default keyboard shortcuts for a command:

{
  "jupyter.lab.shortcuts": [
    {
      "command": "my-command",
      "keys": ["Accel T"],
      "selector": ".jp-mod-searchable"
    }
  ]
}

Shortcuts added to the settings system will be editable by users.

Launcher

As with menus, keyboard shortcuts, and the command palette, new items can be added to the application launcher via commands. You can do this by requesting the ILauncher token in your extension:

launcher.add({
  command: commandID,
  category: 'Other',
  rank: 0
});

In addition to providing a command ID, you also provide a category in which to put your item, (e.g. ‘Notebook’, or ‘Other’), as well as a rank to determine its position among other items.

Jupyter Front-End Shell

The Jupyter front-end shell is used to add and interact with content in the application. The IShell interface provides an add() method for adding widgets to the application. In JupyterLab, the application shell consists of:

• A top area for things like top-level toolbars and information.

• A menu area for top-level menus, which is collapsed into the top area in multiple-document mode and put below it in single-document mode.

• left and right sidebar areas for collapsible content.

• A main work area for user activity.

• A down area for information content; like log console, contextual help.

• A bottom area for things like status bars.

• A header area for custom elements.

Left/Right Areas

The left and right sidebar areas of JupyterLab are intended to host more persistent user interface elements than the main area. That being said, extension authors are free to add whatever components they like to these areas. The outermost-level of the object that you add is expected to be a Lumino Widget, but that can host any content you like (such as React components).

As an example, the following code executes an application command to a terminal widget and then adds the terminal to the right area:

app.commands
  .execute('terminal:create-new')
  .then((terminal: WidgetModuleType.Terminal) => {
    app.shell.add(terminal, 'right');
  });

You can use a numeric rank to control the ordering of the left and right tabs:

app.shell.add(terminal, 'left', {rank: 600});

The recommended ranges for this rank are:

• 0-500: reserved for first-party JupyterLab extensions.

• 501-899: reserved for third-party extensions.

• 900: The default rank if none is specified.

• 1000: The JupyterLab extension manager.

Main Menu

There are two ways to extend JupyterLab’s main menu.

1. Using the settings - this is the preferred way as they are configurable by the user.

2. Using the API - this is for advanced cases like dynamic menu or semantic items.

Settings-defined menu

JupyterLab provides integration with its settings system for menu definitions. Your extension can provide a settings schema with a jupyter.lab.menus key, declaring default menus. You don’t need to set anything in the TypeScript code (except the command definitions).

To add a new menu with your extension command:

{
  "jupyter.lab.menus": {
  "main": [
    {
      "id": "jp-mainmenu-myextension",
      "label": "My Menu",
      "items": [
        {
          "command": "my-command",
          "rank": 500
        }
      ],
      "rank": 100
    }
  ]
}

The menu item label will be set with the command label. For menus (and submenus), the label needs to be set explicitly with the label property.

Menu and item have a rank that will determine the elements order.

To add a new entry in an existing menu:

{
  "jupyter.lab.menus": {
  "main": [
    {
      "id": "jp-mainmenu-file",
      "items": [
        {
          "command": "my-command",
          "rank": 500
        }
      ]
    }
  ]
}

Here is the list of default menu ids:

• File menu: jp-mainmenu-file

  • New file submenu: jp-mainmenu-file-new

• Edit menu: jp-mainmenu-edit

• View menu: jp-mainmenu-view

• Run menu: jp-mainmenu-run

• Kernel menu: jp-mainmenu-kernel

• Tabs menu: jp-mainmenu-tabs

• Settings menu: jp-mainmenu-settings

• Help menu: jp-mainmenu-help

The default main menu is defined in the mainmenu-extension package settings.

A menu must respect the following schema:

    "menu": {
      "properties": {
        "disabled": {
          "description": "Whether the menu is disabled or not",
          "type": "boolean",
          "default": false
        },
        "icon": {
          "description": "Menu icon id",
          "type": "string"
        },
        "id": {
          "description": "Menu unique id",
          "oneOf": [
            {
              "type": "string",
              "enum": [
                "jp-menu-file",
                "jp-menu-file-new",
                "jp-menu-edit",
                "jp-menu-help",
                "jp-menu-kernel",
                "jp-menu-run",
                "jp-menu-settings",
                "jp-menu-view",
                "jp-menu-tabs"
              ]
            },
            { "type": "string", "pattern": "[a-z][a-z0-9\\-_]+" }
          ]
        },
        "items": {
          "description": "Menu items",
          "type": "array",
          "items": {
            "$ref": "#/definitions/menuItem"
          }
        },
        "label": {
          "description": "Menu label",
          "type": "string"
        },
        "mnemonic": {
          "description": "Mnemonic index for the label",
          "type": "number",
          "minimum": -1,
          "default": -1
        },
        "rank": {
          "description": "Menu rank",
          "type": "number",
          "minimum": 0
        }
      },
      "required": ["id"],
      "type": "object"
    },

And an item must follow:

    "menuItem": {
      "properties": {
        "args": {
          "description": "Command arguments",
          "type": "object"
        },
        "command": {
          "description": "Command id",
          "type": "string"
        },
        "disabled": {
          "description": "Whether the item is disabled or not",
          "type": "boolean",
          "default": false
        },
        "type": {
          "description": "Item type",
          "type": "string",
          "enum": ["command", "submenu", "separator"],
          "default": "command"
        },
        "rank": {
          "description": "Item rank",
          "type": "number",
          "minimum": 0
        },
        "submenu": {
          "oneOf": [
            {
              "$ref": "#/definitions/menu"
            },
            {
              "type": "null"
            }
          ]
        }
      },
      "type": "object"
    },

Menus added to the settings system will be editable by users using the mainmenu-extension settings. In particular, they can be disabled at the item or the menu level by setting the property disabled to true.

API-defined menu

To use the API, you should request the IMainMenu token for your extension.

There are three main ways to extend:

1. You can add your own menu to the menu bar.

2. You can add new commands to the existing menus.

3. You can register your extension with one of the existing semantic menu items.

Adding a New Menu

To add a new menu to the menu bar, you need to create a new Lumino menu.

You can then add commands to the menu in a similar way to the command palette, and add that menu to the main menu bar:

const menu = new Menu({ commands: app.commands });
menu.addItem({
  command: commandID,
  args: {},
});

mainMenu.addMenu(menu, { rank: 40 });

As with the command palette, you can optionally pass in args to customize the rendering and execution behavior of the command in the menu context.

Adding a New Command to an Existing Menu

In many cases you will want to add your commands to the existing JupyterLab menus rather than creating a separate menu for your extension. Because the top-level JupyterLab menus are shared among many extensions, the API for adding items is slightly different. In this case, you provide a list of commands and a rank, and these commands will be displayed together in a separate group within an existing menu.

For instance, to add a command group with firstCommandID and secondCommandID to the File menu, you would do the following:

mainMenu.fileMenu.addGroup([
  {
    command: firstCommandID,
  },
  {
    command: secondCommandID,
  }
], 40 /* rank */);

Registering a Semantic Menu Item

There are some commands in the JupyterLab menu system that are considered common and important enough that they are treated differently.

For instance, we anticipate that many activities may want to provide a command to close themselves and perform some cleanup operation (like closing a console and shutting down its kernel). Rather than having a proliferation of similar menu items for this common operation of “closing-and-cleanup”, we provide a single command that can adapt itself to this use case, which we term a “semantic menu item”. For this example, it is the File Menu closeAndCleaners set.

Here is an example of using the closeAndCleaners semantic menu item:

mainMenu.fileMenu.closeAndCleaners.add({
  tracker,
  action: 'Shutdown',
  name: 'My Activity',
  closeAndCleanup: current => {
    current.close();
    return current.shutdown();
  }
});

In this example, tracker is a Widget Tracker, which allows the menu item to determine whether to delegate the menu command to your activity, name is a name given to your activity in the menu label, action is a verb given to the cleanup operation in the menu label, and closeAndCleanup is the actual function that performs the cleanup operation. So if the current application activity is held in the tracker, then the menu item will show Shutdown My Activity, and delegate to the closeAndCleanup function that was provided.

More examples for how to register semantic menu items are found throughout the JupyterLab code base. The available semantic menu items are:

• IEditMenu.IUndoer: an activity that knows how to undo and redo.

• IEditMenu.IClearer: an activity that knows how to clear its content.

• IEditMenu.IGoToLiner: an activity that knows how to jump to a given line.

• IFileMenu.ICloseAndCleaner: an activity that knows how to close and clean up after itself.

• IFileMenu.IConsoleCreator: an activity that knows how to create an attached code console for itself.

• IHelpMenu.IKernelUser: an activity that knows how to get a related kernel session.

• IKernelMenu.IKernelUser: an activity that can perform various kernel-related operations.

• IRunMenu.ICodeRunner: an activity that can run code from its content.

• IViewMenu.IEditorViewer: an activity that knows how to set various view-related options on a text editor that it owns.

Status Bar

JupyterLab’s status bar is intended to show small pieces of contextual information. Like the left and right areas, it only expects a Lumino Widget, which might contain any kind of content. Since the status bar has limited space, you should endeavor to only add small widgets to it.

The following example shows how to place a status item that displays the current “busy” status for the application. This information is available from the ILabStatus token, which we reference by a variable named labStatus. We place the statusWidget in the middle of the status bar. When the labStatus busy state changes, we update the text content of the statusWidget to reflect that.

const statusWidget = new Widget();
labStatus.busySignal.connect(() => {
  statusWidget.node.textContent = labStatus.isBusy ? 'Busy' : 'Idle';
});
statusBar.registerStatusItem('lab-status', {
  align: 'middle',
  item: statusWidget
});

Toolbar Registry

JupyterLab provides an infrastructure to define and customize toolbar widgets of DocumentWidget s from the settings, which is similar to that defining the context menu and the main menu bar. A typical example is the notebook toolbar as in the snippet below:

function activatePlugin(
  app: JupyterFrontEnd,
  // ...
  toolbarRegistry: IToolbarWidgetRegistry | null,
  settingRegistry: ISettingRegistry | null
): NotebookWidgetFactory.IFactory {
  const { commands } = app;
  let toolbarFactory:
    | ((widget: NotebookPanel) => DocumentRegistry.IToolbarItem[])
    | undefined;

  // Register notebook toolbar specific widgets
  if (toolbarRegistry) {
    toolbarRegistry.registerFactory<NotebookPanel>(FACTORY, 'cellType', panel =>
      ToolbarItems.createCellTypeItem(panel, translator)
    );

    toolbarRegistry.registerFactory<NotebookPanel>(
      FACTORY,
      'kernelStatus',
      panel => Toolbar.createKernelStatusItem(panel.sessionContext, translator)
    );
    // etc...

    if (settingRegistry) {
      // Create the factory
      toolbarFactory = createToolbarFactory(
        toolbarRegistry,
        settingRegistry,
        // Factory name
        FACTORY,
        // Setting id in which the toolbar items are defined
        '@jupyterlab/notebook-extension:panel',
        translator
      );
    }
  }

  const factory = new NotebookWidgetFactory({
    name: FACTORY,
    fileTypes: ['notebook'],
    modelName: 'notebook',
    defaultFor: ['notebook'],
    // ...
    toolbarFactory,
    translator: translator
  });
  app.docRegistry.addWidgetFactory(factory);

The registry registerFactory method allows an extension to provide special widget for a unique pair (factory name, toolbar item name). Then the helper createToolbarFactory can be used to extract the toolbar definition from the settings and build the factory to pass to the widget factory.

The default toolbar items can be defined across multiple extensions by providing an entry in the "jupyter.lab.toolbars" mapping. For example for the notebook panel:

"jupyter.lab.toolbars": {
  "Notebook": [ // Factory name
    // Item with non-default widget - it must be registered within an extension
    {
      "name": "save", // Unique toolbar item name
      "rank": 10 // Item rank
    },
    // Item with default button widget triggering a command
    { "name": "insert", "command": "notebook:insert-cell-below", "rank": 20 },
    { "name": "cut", "command": "notebook:cut-cell", "rank": 21 },
    { "name": "copy", "command": "notebook:copy-cell", "rank": 22 },
    { "name": "paste", "command": "notebook:paste-cell-below", "rank": 23 },
    { "name": "run", "command": "runmenu:run", "rank": 30 },
    { "name": "interrupt", "command": "kernelmenu:interrupt", "rank": 31 },
    { "name": "restart", "command": "kernelmenu:restart", "rank": 32 },
    {
      "name": "restart-and-run",
      "command": "runmenu:restart-and-run-all",
      "rank": 33 // The default rank is 50
    },
    { "name": "cellType", "rank": 40 },
    // Horizontal spacer widget
    { "name": "spacer", "type": "spacer", "rank": 100 },
    { "name": "kernelName", "rank": 1000 },
    { "name": "kernelStatus", "rank": 1001 }
  ]
},
"jupyter.lab.transform": true,
"properties": {
  "toolbar": {
    "title": "Notebook panel toolbar items",
    "items": {
      "$ref": "#/definitions/toolbarItem"
    },
    "type": "array",
    "default": []
  }
}

The settings registry will merge those definitions from settings schema with any user-provided overrides (customizations) transparently and save them under the toolbar property in the final settings object. The toolbar list will be used to create the toolbar. Both the source settings schema and the final settings object are identified by the plugin ID passed to createToolbarFactory. The user can customize the toolbar by adding new items or overriding existing ones (like providing a different rank or adding "disabled": true to remove the item).

Note

You need to set jupyter.lab.transform to true in the plugin id that will gather all items.

The current widget factories supporting the toolbar customization are:

• Notebook: Notebook panel toolbar

• Editor: Text editor toolbar

• HTML Viewer: HTML Viewer toolbar

• CSVTable: CSV (Comma Separated Value) Viewer toolbar

• TSVTable: TSV (Tabulation Separated Value) Viewer toolbar

Add the toolbar item must follow this definition:

        },
        "disabled": {
          "description": "Whether this shortcut is disabled or not.",
          "type": "boolean",
          "default": false
        },
        "keys": {
          "title": "The key sequence for the binding",
          "description": "The key shortcut like `Accel A` or the sequence of shortcuts to press like [`Accel A`, `B`]",
          "items": {
            "type": "string"
          },
          "type": "array"
        },
        "macKeys": {
          "title": "The key sequence for the binding on macOS",
          "description": "The key shortcut like `Cmd A` or the sequence of shortcuts to press like [`Cmd A`, `B`]",
          "items": {
            "type": "string"
          },
          "type": "array"
        },
        "winKeys": {
          "title": "The key sequence for the binding on Windows",
          "description": "The key shortcut like `Ctrl A` or the sequence of shortcuts to press like [`Ctrl A`, `B`]",
          "items": {
            "type": "string"
          },
          "type": "array"
        },
        "linuxKeys": {
          "title": "The key sequence for the binding on Linux",
          "description": "The key shortcut like `Ctrl A` or the sequence of shortcuts to press like [`Ctrl A`, `B`]",
          "items": {
            "type": "string"
          },
          "type": "array"
        },
        "selector": {
          "title": "CSS selector",
          "type": "string"
        }
      },
      "required": ["command", "keys", "selector"],
      "type": "object"
    },

Widget Tracker

Often extensions will want to interact with documents and activities created by other extensions. For instance, an extension may want to inject some text into a notebook cell, or set a custom keymap, or close all documents of a certain type. Actions like these are typically done by widget trackers. Extensions keep track of instances of their activities in WidgetTrackers, which are then provided as tokens so that other extensions may request them.

For instance, if you want to interact with notebooks, you should request the INotebookTracker token. You can then use this tracker to iterate over, filter, and search all open notebooks. You can also use it to be notified via signals when notebooks are added and removed from the tracker.

Widget tracker tokens are provided for many activities in JupyterLab, including notebooks, consoles, text files, mime documents, and terminals. If you are adding your own activities to JupyterLab, you might consider providing a WidgetTracker token of your own, so that other extensions can make use of it.

State Database

The state database can be accessed by importing IStateDB from @jupyterlab/statedb and adding it to the list of requires for a plugin:

const id = 'foo-extension:IFoo';

const IFoo = new Token<IFoo>(id);

interface IFoo {}

class Foo implements IFoo {}

const plugin: JupyterFrontEndPlugin<IFoo> = {
  id,
  autoStart: true,
  requires: [IStateDB],
  provides: IFoo,
  activate: (app: JupyterFrontEnd, state: IStateDB): IFoo => {
    const foo = new Foo();
    const key = `${id}:some-attribute`;

    // Load the saved plugin state and apply it once the app
    // has finished restoring its former layout.
    Promise.all([state.fetch(key), app.restored])
      .then(([saved]) => { /* Update `foo` with `saved`. */ });

    // Fulfill the plugin contract by returning an `IFoo`.
    return foo;
  }
};