--save flag for npm adds the package to the dependencies in package.json
Since npm 5.0.0 —save is now the default behavior so it doesn’t have been run explicitly anymore
--save-dev flag for npm adds the package to dev dependencies instead of dependencies
The reason for this is because some packages aren’t used during run-time and are used to parse/lint the code
When you run npm install --production the installation process will skip dev dependencies to reduce the bloat for prod ready environment