Avoid creating a separate file for component controllers.
Imagine that the component and controller were in separate in the above
example. Then, it wouldn’t be obvious why the state is necessary just by
looking at the component file, since there are no calls to updateState in the
It may be tempting to split the component controller into its own file in order
to make the file less than 300 lines, but we think it’s worse to have the
component controller in its own file.