README.md

Cell Toolbar Button

This example shows how to add buttons to the cell toolbar. The buttons are displayed or not, depending on the cell type.

In this particular example, the buttons will execute a code cell, or render a markdown cell.

The command to run is already defined (notebook:run-cell), but we need to create new commands to display or not the button, depending on the cell type.

To add a button triggering a command to the cell toolbar, you must specified the following settings:

// schema/plugin.json#L8-L19

"jupyter.lab.toolbars": {
  "Cell": [
    {
      "name": "run-code-cell",
      "command": "toolbar-button:run-code-cell"
    },
    {
      "name": "render-markdows-cell",
      "command": "toolbar-button:render-markdown-cell"
    }
  ]
}

The key Cell inform JupyterLab about which widget toolbar should be extended. The name should be an unique identifier for the widget toolbar items. The command is the unique command identifier.

The commands name are defined in the src/index.ts file:

// src/index.ts#L8-L17

const CommandIds = {
  /**
   * Command to render a markdown cell.
   */
  renderMarkdownCell: 'toolbar-button:render-markdown-cell',
  /**
   * Command to run a code cell.
   */
  runCodeCell: 'toolbar-button:run-code-cell'
};

And the commands are created when the extension is activated:

// src/index.ts#L30-L48

/* Adds a command enabled only on code cell */
commands.addCommand(CommandIds.runCodeCell, {
  icon: runIcon,
  caption: 'Run a code cell',
  execute: () => {
    commands.execute('notebook:run-cell');
  },
  isVisible: () => tracker.activeCell?.model.type === 'code'
});

/* Adds a command enabled only on markdown cell */
commands.addCommand(CommandIds.renderMarkdownCell, {
  icon: markdownIcon,
  caption: 'Render a markdown cell',
  execute: () => {
    commands.execute('notebook:run-cell');
  },
  isVisible: () => tracker.activeCell?.model.type === 'markdown'
});

The following line will add the class lm-mod-hidden to the button if the active cell is not a code cell:

// src/index.ts#L37-L37

isVisible: () => tracker.activeCell?.model.type === 'code'

To hide the button, we need to add a CSS rule on the class lm-mod-hidden in the file style/base.css:

.jp-ToolbarButtonComponent.lm-mod-hidden {
  display: none;
}

Where to Go Next

This example uses a command to display the widget. Have a look a the commands example for more information about it.