We all know that Greenfield software development is rare, and that makes the examples used in this talk very practical. An application system used to be based on React for its frontend needs, but it was converted to Svelte. Oli shows practical examples of the required steps. Partly this is about replacing individual components, but integration is also important: how easy is it to use existing data services, and does all state management need to be reimplemented? Demonstrations include the role of SvelteKit, which offers some potential solutions with its data service functionality.