By "supporting typescript" it parses typescript code and won't fail. That is what a bundler promises. Bundler doesn't have to do the typechecking. It is actually conventional to set it up that way for any bundler. In my job we have webpack bundling typescript with babel in the "build" step. We could've use ts-loader but we want hot reload to be fast. Then in the "check" step we have ts, linter, unit tests. Those run on CI.