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Maven stores all of the artifacts that it retrieves in one big local cache so that you don't have to pull the same dependency down.

NPM, by default, will store the artifacts into a directory local to your project.

The maven way sounds nice, but it's easy to possible to screw things up between different projects. (Especially if you have mvn 2 and mvn 3 projects, ugh).

With NPM, everything is nice and separated.

Ivy is like a mix of the two (a global local cache, but pulls down to the local project), which IMHO, has the benefit of neither while getting the drawbacks of both.

[chinpokomon]

How is it easy to screw things up? You specify the version of a dependency when you write each POM file. If there are two projects, each with different dependency versions, they only get the dependency version they requested. Only if you have two different dependencies that report themselves as having the same Maven coordinate, that is to say the same Group Id, Artifact Id, and Version number, will you have any problems. But then that isn't a "Maven" problem insomuch as it is a bad dependency.