Can run one specific version of TS, and JS that has been compiled from any version of TS. That ability might be very valuable for the development loop, but it

Can run one specific version of TS, and JS that has been compiled from any version of TS. That ability might be very valuable for the development loop, but it cannot be intended for dependencies because source compatibility is very low in the priorities list of TS. In JVM words: where scala seems to have given up on cross-version compatibility of the complied code, forcing cross building upon library authors and dependency registries but succeeds in sufficient source compatibility to enable that cross building, TS, due to being bound to baseline JS as output anyways, does the inverse. The output works across versions (how could it not, when it's meant to work across languages), but with that a given it can take its liberties with input (source) compatibility.