I agree in general that debugging js in dev environment is easier using breakpoints and watchmode but in reality when you are in production the code is usually minified and putting breakpoints in JS could be painful and sometimes crashes also Chrome for example (especially if you want to debug differente breakpoints/resizing a window / testing media query).

Besides this there is another issue, when you add a breakpoint, many async callbacks reach timeout, so this changes also the normal workflow of a web application…