How to use npm global without sudo on OSX from http://www.johnpapa.net/how-to-use-npm-global-without-sudo-on-osx/

sudofreenpm

This removes, forcefully, everything in the old npm folders.
sudo rm -rf /usr/local/lib/node_modules
sudo rm -rf ~/.npm

This removes node and puts it back without npm
brew uninstall node

For advanced users, the rest of these can be run via copy and paste into terminal.

brew install node --without-npm
mkdir "${HOME}/.npm-packages"
echo NPM_PACKAGES="${HOME}/.npm-packages" >> ${HOME}/.bashrc
echo prefix=${HOME}/.npm-packages >> ${HOME}/.npmrc
curl -L https://www.npmjs.org/install.sh | sh
echo NODE_PATH=\"\$NPM_PACKAGES/lib/node_modules:\$NODE_PATH\" >> ${HOME}/.bashrc
echo PATH=\"\$NPM_PACKAGES/bin:\$PATH\" >> ${HOME}/.bashrc
echo source "~/.bashrc" >> ${HOME}/.bash_profile
source ~/.bashrc