This article tells about not using sudo for npm…
This is caused by using sudo to install the first package.
This causes the ~/.npm cache folder with root permissions which means that all subsequent installs also require root permissions.
You can read more here on that and how to resolve it:
NOTE: I have written a new post explaining how to do this better and easier using nvm The problem A lot of people…www.competa.com
A better way is to use nvm and this article tells how to do that.