There really is a right or wrong way per se.
My personal preference usually is 1 script file per entity - named something like xxx_case (the xxx being the prefix of my solution) and then any scripts I might reuse on different entities in another file (like phone number formatting) xxx_common.
You can split your scripts into multiple files if that makes it easier to read later. Just be careful you don't accidentally have the same method name used in both files, only the method in the file loaded last will get used. if you if you start loading multiple files technically this would be more of a performance hit then 1 large file just based on the number of requests being made but it probably wouldn't be noticeable unless you're dealing with a ton of script.