There is generally no typing in run time. One of the practices in writing compilers is to skip type checks during run time, because you know beforehand that no type errors are possible. That is type erasure.
If you're interested, lookup existential types. Very interesting stuff.
There are however javascript libraries which allow you specify object schemas and throw errors when mismatches occur. Perhaps the suggestion then is to build some shared layer between the TS compiler and V8 so that similar schemas can be autogenerated by the TS compiler and enforced at run-time.