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