vagrant-cachier-ng/docs/buckets/npm.md

npm

Compatible with probably any type of linux guest distro, will hook into npm's cache directory under the result of running npm config get cache as the default SSH user (usually vagrant) on your guest.

To manually enable it:

Vagrant.configure("2") do |config|
  config.vm.box = 'some-box-with-nodejs-installed'
  config.cache.enable :npm
end

If you use nvm / n on the guest machine, make sure it is already installed before enabling the bucket, otherwise you won't benefit from this plugin.