How to correctly extend the React components?

First, please don't try to persuade to use the React Hooks API. I need and want the class API, and that's it.

In below React class component, the PartialsFlags is the associative array-like object which depends on specific inheritor. From the viewpoint of JavaScript/JSX, above components are completely valid, and although I have omitted the return value in render method of AdmonitionBlockGallery class, I have checked that components has been rendered correctly.