Grab the latest brew before we start
$ brew update
Updated Homebrew from 951fb108 to f0b70e57.
Updated 3 taps (homebrew/fuse, homebrew/games, pivotal/tap).
==> Migrating Homebrew to v0.9.9
...install npm
$ brew install npm
==> Downloading https://homebrew.bintray.com/bottles/node-6.1.0.el_capitan.bottle.tar.gz
######################################################################## 100.0%
==> Pouring node-6.1.0.el_capitan.bottle.tar.gz
....
==> Summary
🍺 /usr/local/Cellar/node/6.1.0: 3,655 files, 38.6M
...Cheers npm 3.8.6
$ npm --version
3.8.6