Microsoft Research is working on a project called “Safer TypeScript”.
At the moment it is unclear how the new type-checker works.
Developers can activate the new type-checker via a compiler flag.
When using plain TypeScript, you only get type safety at compile time, not runtime type safety which Safer TypeScript addresses.
The project is still in its early days and just a research project, so it is not ready for production use yet – but it already looks very promising.