Having no understanding of the broader js context I assumed the comment to mean "all library dependencies should be checked in, build tools should be defined & specified & able to fully recreate the build given they are installed".
For the record this is a well known & frequently advocated for build pattern.
Fair enough, I guess I was just thinking of the issue I'd run into with trying to actually install anything in the first place.
In the case of npm though, installation brings down a lot of files so it's not super efficient. I've installed 15 packages and have over 12,000 files (75MB) to show for it.