From a refactoring perspective, typechecking makes the answer to the question "What is this change going to break?" much more obvious.
Combine that with Typescript's IDE support and a lot of the usual dumb refactoring mistakes just don't happen so you can focus on the actual algorithmic problems emerging.
Combine that with Typescript's IDE support and a lot of the usual dumb refactoring mistakes just don't happen so you can focus on the actual algorithmic problems emerging.