npm install -g webpack gives tar.unpack untar error - node.js

Question

I created a new user on my Mac and tried this. This normally works in my other account. This new user is an administrator also.
npm ERR! tar.unpack untar error /Users/test/.npm/webpack/1.11.0/package.tgz
npm ERR! Darwin 14.4.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "webpack"
npm ERR! node v0.12.4
npm ERR! npm v2.10.1
npm ERR! path /usr/local/lib/node_modules/webpack
npm ERR! code EACCES
npm ERR! errno -13
npm ERR! Error: EACCES, mkdir '/usr/local/lib/node_modules/webpack'
npm ERR! at Error (native)
npm ERR! { [Error: EACCES, mkdir '/usr/local/lib/node_modules/webpack']
npm ERR! errno: -13,
npm ERR! code: 'EACCES',
npm ERR! path: '/usr/local/lib/node_modules/webpack',
npm ERR! fstream_type: 'Directory',
npm ERR! fstream_path: '/usr/local/lib/node_modules/webpack',
npm ERR! fstream_class: 'DirWriter',
npm ERR! fstream_stack:
npm ERR! [ '/usr/local/lib/node_modules/npm/node_modules/fstream/lib/dir-writer.js:35:25',
npm ERR! '/usr/local/lib/node_modules/npm/node_modules/mkdirp/index.js:47:53',
npm ERR! 'FSReqWrap.oncomplete (fs.js:95:15)' ] }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.
npm ERR! Please include the following file with any support request:
npm ERR! /Users/test/WebstormProjects/babel-test/npm-debug.log
I am not very good with the UNIX stuff and things, I just wish these things would be more easy.

Answer 1

From the looks of it, since it says EACCES, it is probably getting an access denied from the system. If you are installing globally on unix you must use sudo.
$ sudo npm install -g webpack

Answer 2

Start using nvm and it will save you from using sudo at all.
https://github.com/creationix/nvm