9. Block Extensions

A common pattern in blocks is the "variations" UI pattern - a slightly different versions of a block that can be toggled on demand by the editors. Choosing the listing template (gallery, summary listing, etc.) for the Listing block is one example of the typical use case for this feature.

A block defines variations in its block configuration. These variations can be used to enhance or complement the default behavior of a block without having to shadow its stock components. These enhancements can be at the settings level (add or remove block settings) via schema enhancers or, if the code of your block allows it, even use alternative renderers (e.g., in view mode) showing the enhanced fields or modifying the block behavior or look and feel.

export default (config) => {
  config.blocks.blocksConfig.teaserBlock.variations = [
    {
      id: 'default',
      title: 'Default',
      isDefault: true,
      template: SimpleTeaserView
    },
    {
      id: 'card',
      label: 'Card',
      template: CardTeaserView,
      schemaEnhancer: ({schema, formData, intl}) => {
        schema.properties.cardSize = '...'; // fill in your implementation
        return schema;
      }
    }
  ];
}

The capabilities of a block can't be constrained only to the "variations". What if, for example, one such variation is so advanced that it needs its own "variations"? So the variations are simply a more concrete example of a Volto block extension.

Volto provides several helpers to manage the extensions:

• resolveBlockExtensions, a function that resolves extensions (all available extensions for that blockandresolvedExtensions` (the current active extensions of that block)

• withBlockExtensions, a React HOC uses the resolveBlockExtensions to inject extensions and resolvedExtensions as block props

• withBlockSchemaEnhancer which bootstraps the variation mechanism (by providing a select control to toggle the active variation) and use any defined schemaEnhancer for the block

• withVariationSchemaEnhancer, a React HOC which uses the defined schemaEnhancer from the active block variation to mutate the schema.

• withStylingSchemaEnhancer, a similar HOC which enhances the schema with information from the stylesSchema. These 2 helpers are directly wrapped over the InlineForm to create the BlockDataForm component.