We discuss two adaptations of the implementation of type guards and narrowing in the TypeScript compiler. The first is an improvement on the original syntax-directed implementation, and has now replaced the original one in the TypeScript compiler. It is specifically suited for the scenario in which an IDE requests the type of a particular variable in the program. The second implementation is defined as a whole program analysis, and is therefore able to compute more precise narrowed types, but at the price of a higher run-time cost