A big problem I have run into on projects that have gathered dust for a few months has been when version wasn't pinned, or the package wasn't using semver, or some other drift in the package.json that causes a slightly or completely newer version to come down, which causes, a whole host of dependencies to update and then boom- hopefully you have unit tests to catch the breaking changes.
Also, when you check the project out and it was relying on global npm packages to build and the system you're working on has been updated in the last few months and now all of a sudden your grunt file doesn't run or your CSS minimizer complains about your Ruby version. God forbid you build multiple JS projects in one CI server!
Also, when you check the project out and it was relying on global npm packages to build and the system you're working on has been updated in the last few months and now all of a sudden your grunt file doesn't run or your CSS minimizer complains about your Ruby version. God forbid you build multiple JS projects in one CI server!