Too Long; Didn't Read
The JavaScript ecosystem moves fast and most tools, frameworks & libraries are updated quite frequently. Most libraries release minor updates (e.g.x.2.3.x/2.4) every month and major updates with breaking changes every 6 to 12 months. As a rule of thumb, you should update your application’s dependencies at least once every quarter. Redundunded unused dependencies should be updated while updating. React Router v4 is a complete rewrite and several new features and bug fixes are still being added with every release.