Event

This document introduces the handling of UI events, event flows within the block tree, and the implementation of hotkeys in BlockSuite.

Handling UI Events

For UI events such as click in editor, there is an underlying event dispatcher in @blocksuite/block-std to dispatch events. With the dispatcher, you can handle events in your block view implementation in this manner:

@customElements('my-block')
class MyBlockView extends BlockElement<MyBlockModel> {
  private _handleClick = () => {
    //...
  };

  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick);
  }
}

Event Bubbling

All events on dispatcher are bound to the root element of the block view to make it possible to bubble events to the parent block view.

class ChildView extends BlockElement<MyBlockModel> {
  private _handleClick = () => {
    console.log('click1');
  };

  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick);
  }
}

class ParentView extends BlockElement<MyBlockModel> {
  private _handleClick = () => {
    console.log('click2');
  };

  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick);
  }
}

When you click on the ChildView, the console will print:

click1
click2

You may want to stop the event from bubbling to the parent block view. You can simply return true in the event handler:

class ChildView extends BlockElement<MyBlockModel> {
  private _handleClick = () => {
    console.log('click1');
    return true;
  };

  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick);
  }
}

Then the console will only print:

click1

The event bubbling is implemented by event target. For the events that won't support bubbling, the event dispatcher will use block path to dispatch events to the parent block views.

Event Scope

By default, handleEvents will only subscribe events triggered by the block view and its children. We also provide two more scopes to subscribe to make it possible to handle events triggered by other blocks.

Flavour Scope

The flavour scope will subscribe to events triggered by the block view and other blocks with the same flavour.

class MyBlock extends BlockElement<MyBlockModel> {
  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick, { flavour: true });
  }
}

Global Scope

The global scope will subscribe to events triggered by the block view and all other blocks.

class MyBlock extends BlockElement<MyBlockModel> {
  override connectedCallback() {
    super.connectedCallback();
    this.handleEvent('click', this._handleClick, { global: true });
  }
}

Handling Hotkeys

The hotkey is a special event that can be triggered by the keyboard.

Key names may be strings like "Shift-Ctrl-Enter"—a key identifier prefixed with zero or more modifiers. Key identifiers are based on the strings that can appear in KeyEvent.key.

Use lowercase letters to refer to letter keys (or uppercase letters if you want shift to be held). You may use "Space" as an alias for the " " name.

Modifiers can be given in any order. Shift- (or s-), Alt- (or a-), Ctrl- (or c- or Control-) and Cmd- (or m- or Meta-) are recognized. For characters that are created by holding shift, the Shift- prefix is implied, and should not be added explicitly.

You can use Mod- as a shorthand for Cmd- on Mac and Ctrl- on other platforms.

class MyBlock extends BlockElement<MyBlockModel> {
  override connectedCallback() {
    super.connectedCallback();
    this.bindHotkey({
      'Mod-b': () => {},
      'Alt-Space': () => {},
    });
  }
}

Same as handleEvent, you can return true in the hotkey handler to stop the event from bubbling to the parent block view.