If you're doing local development you may have local libraries that you've linked. It makes development easier than having to publish out the library and do a new npm install on the main project using it just to test changes.

I an dealing with three libraries or so on a current project and wanted to know which ones are linked. You can get this by running this command:

view plain print about
1npm ls -g --depth=0 --link=true

It worked great and told me exactly what I needed.

If you're on Windows, you can also open this directory to see the sim linked libs:

view plain print about
1C:\Users\[username]\AppData\Roaming\npm\node_modules

I assume a similar directory exists on Macs.