Recently, I upgraded to the latest NodeJS/npm and npm stopped working. It turns out that there was a problem with the OSX installer.
After painful amounts of googling, I found that some had solved it by "tracking down" the node and npm files, removing them and then reinstalling with the node distribution download (dmg) from nodejs.org.
I tracked down the files. Do this:
sudo rm -rf /usr/local/bin/node
sudo rm /usr/local/bin/npm
sudo rm -rf /usr/local/lib/node_modules/npm
And then hit up http://nodejs.org for a new installer. You will have a fresh working installation.
PS, the problem with npm was this:
When I typed
npm init
to start up a node module, I got errors that included
Error: Cannot find module 'github-url-from-git'
Turns out that basically everything I did with npm except --version was broken in this way.
The 'delete before reinstalling' process listed above fixed it.