Sapper rates a 5 out of 7 on the Sam Saccone Scale. We don't have in-component type checking yet (high priority post-v3), and maintaining a roadmap hasn't really been our forté, but we've got the rest down
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My table stakes in 2019 for picking a front-end toolkit/framework
1. code splitting by default
2. server side rendering
3. baked in opinionated data-binding
4. can render lists > 1K items w/o making my computer 💩
5. strict type checking
6. has a 1+ year roadmap
7. a router