It appears that the backend is written in TS, while the frontend in JS. Personally I separate church and state by writing tests in JS and application code in T

It appears that the backend is written in TS, while the frontend in JS. Personally I separate church and state by writing tests in JS and application code in TS. If you're asking why these languages at all when this and that other language is faster, most likely it's less of a bottleneck than estimated.