Sapper

Sapper is a framework for building high-performance web applications with Svelte, offering server-side rendering, routing, and code-splitting out of the box. It was the official application framework for Svelte before being succeeded by SvelteKit. Sapper enabled developers to build fast, SEO-friendly applications by rendering pages on the server initially and then taking over in the browser as a single-page application. It included file-based routing, automatic code splitting, and offline support through service workers. The framework provided both static site generation and server-side rendering options, giving developers flexibility in deployment strategies. Sapper simplified common application concerns like navigation, prefetching, and state management. While officially deprecated in favor of SvelteKit, Sapper laid important groundwork for Svelte's application development patterns and many existing applications continue to use it.