If you just want to fix the issue quickly, scroll down to the "solution" section below.
If you're a Mac Homebrew user and you installed node via Homebrew, there is a major philosophical issue with the way Homebrew and NPM work together. If you install node with Homebrew and then try to do npm update npm -g, you will see an error like this:
$ npm update npm -g
| echo 'export PATH=$HOME/local/bin:$PATH' >> ~/.bashrc | |
| . ~/.bashrc | |
| mkdir ~/local | |
| mkdir ~/node-latest-install | |
| cd ~/node-latest-install | |
| curl http://nodejs.org/dist/node-latest.tar.gz | tar xz --strip-components=1 | |
| ./configure --prefix=~/local | |
| make install # ok, fine, this step probably takes more than 30 seconds... | |
| curl https://www.npmjs.org/install.sh | sh |
| // Use Gists to store code you would like to remember later on | |
| console.log(window); // log the "window" object to the console |