# install as devDependency
npm install <package-name> --save-dev
# install as normal dependency
npm install <package-name> --save
# install all devDependencies listed in package.json
npm install --only=dev
# install all normal dependencies listed in package.json
npm install --only=prod
# or if NODE_ENV is set to production
npm install
npm i -D
npm install <package-name> --save-dev
npm install --only=prod