NPM won't install any package on Mac. New, clean build. `EACCES` & other errors

By the way, I solved this issue by changing the owner of /usr/local to be myself, in order to allow NPM to modules in its default location without further requiring sudo for each package's installation.

sudo chown -R `whoami` /usr/local

EACCES is an error of not having access on doing an operation.

Taken the line: npm ERR! Error: EACCES, mkdir '/usr/local/lib/node_modules/bower' we can see that npm was unable to create a directory in the given location.

The reason is very likely that you are not running the command as super user. In fact, the error log is even suggesting that:

npm ERR! Please try running this command again as root/Administrator.

To run as administrator, you have to prefix those commands with sudo. That is:

sudo npm install -g bower. You will be required to type in a password for security reasons.