The following command will give you a string of all the npm packages and their versions that are currenctly globally installed.
Note: that this ignores packages installed from directories and picks only those installed via the npm registry.
$ npm ls -g --depth 0 | sed -e '1d' -e 's/└── //g' -e 's/├── //g' -e '/^.*->.*$/d' -e '/^$/d' | tr '\n' ' 'If you copy this string, you can then append it to the end of npm install -g to install all of the packages.