If you want to see how changes to the library affect your project you can map library’s node module to the library’s sources. In that case you don’t need to reinstall library to see the changes. Solution is npm-link.

cd ~/projects/node-redis    # go into the package directory
npm link                    # creates global link
cd ~/projects/node-bloggy   # go into some other package directory.
npm link redis              # link-install the package

More details in official docu