Server-side rendering for async blocks

By default blocks that depend on async-fetched data won't be rendered fully in the server-side rendering phase. For the main "content", Volto provides a mechanism for async rendering in the form of asyncConnect and asyncPropExtenders.

For blocks we have a similar mechanism but we provide it via the config.blocks registry. To use it, add the getAsyncData key in your block configuration, pointing to a function that returns a list of promises.

For example:

export default ({ dispatch, id, data, path }) => {
  return [
    dispatch(
      getQueryStringResults(path, { ...data, fullobjects: 1 }, id),
    ),
  ];
};

All promises returned will be awaited before the rendering of that block, so the strategy is to dispatch the data-fetching actions so that the Redux store gets populated.