Halogens typically do receive priority over alkyl substituents when you can number a parent chain either of two ways resulting in the same locants (numbers) on the substituents. See the examples below:
The left compound would not be 2-methyl-4-chloropentane because chlorine is alphabetically before methyl. The middle compound is not 2-chloro-4-bromopentane for the same reason. The rightmost example would lead some to argue which receives priority, the higher atomic number substituent or the earliest alphabetical substituent. The Chemical Abstracts Service (CAS), an authority in archiving all chemical compounds known, lists this molecule as 1-chloro-2-iodoethane, which would necessitate alphabetical priority being used.