UglifyJS does a lot of dead code elimination. Lots of stuff that only runs on dev environments isn't even included in the production build. Stuff like: if

UglifyJS does a lot of dead code elimination. Lots of stuff that only runs on dev environments isn't even included in the production build. Stuff like: if (process.env.NODE_ENV !== 'production') { invariant(x, y); console.info(z); }