CastMyCode installation error - npm

Question

I try to install CastMyCode on my machine using this command: npm install -g castmycode
Unfortunately, I got this error message:
npm WARN locking Error: EACCES, open '/Users/zulhilmizainudin/.npm/_locks/castmycode-603889af8ee0127d.lock'
npm WARN locking at Error (native)
npm WARN locking /Users/zulhilmizainudin/.npm/_locks/castmycode-603889af8ee0127d.lock failed { [Error: EACCES, open '/Users/zulhilmizainudin/.npm/_locks/castmycode-603889af8ee0127d.lock']
npm WARN locking errno: -13,
npm WARN locking code: 'EACCES',
npm WARN locking path: '/Users/zulhilmizainudin/.npm/_locks/castmycode-603889af8ee0127d.lock' }
npm ERR! Darwin 14.1.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "castmycode"
npm ERR! node v0.12.0
npm ERR! npm v2.6.1
npm ERR! Attempt to unlock /usr/local/lib/node_modules/castmycode, which hasn't been locked
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR! <http://github.com/npm/npm/issues>
npm ERR! Please include the following file with any support request:
npm ERR! /Users/zulhilmizainudin/npm-debug.log
I'm using NPM v2.6.1.
Btw, for those of you that don't know what CastMyCode is, it's actually a simple web app that allow anybody to share their codes and let others view their codes.
It's built by one of my friend. If you're programming mentor/lecturer, CastMyCode can help your students see all your codes changes right inside their web browsers.

Answer 1

Solved. I run this 2 commands inside my terminal:
sudo chown -R $USER ~/.npm
sudo chown -R $USER /usr/local/lib/node_modules
Then I run this command:
npm install -g castmycode
CastMyCode now successfully installed & I can use it. Thanks IBam for sharing the solution!