I'm trying to setup FireBase functions, and when I use the command
npm firebase init functions
Turns out, all you had to do was update your Firebase CLI tools, and downgrade the npm version.
I solved the issue by downgrading my NodeJS to v6.11.0.
Also, I updated my FireBase CLI by running
npm install -g firebase-tools
Use nvm-windows as a version controller for your npm.
Should do the trick.