To minimize the chance of permissions errors, you can configure npm to use a different directory. In this example, it will be a hidden directory on your home folder.

Make a directory for global installations:

 mkdir ~/.npm-global

Configure npm to use the new directory path:

 npm config set prefix '~/.npm-global'

Open or create a ~/.profile file and add this line:

 export PATH=~/.npm-global/bin:$PATH

Back on the command line, update your system variables:

 source ~/.profile

Test: Download a package globally without using sudo.

npm install -g jshint

If still show permission error run (mac os):

sudo chown -R $USER ~/.npm-global