Just like we use NPM for managing Node.js modules (which are stored in the node_modules folder), we use Bower (available at http://bower.io/) for managing dependencies on the frontend (which are stored in the bower_components folder). Suppose you want to use UnderscoreJS (available at http://underscorejs.org/), you can install it using the following command:

bower install underscore

This will download underscore in the bower_components folder, but it doesn't make changes to the bower.json file. However, we want that if any other team member pulls the latest source code, he too should get a copy of underscore on his machine. So we can run the following code:

bower install underscore --save

This adds an entry for underscore in the dependencies section of the bower.json file. However, if we want to install it as a dev-dependency, we need to run the following code:

bower install underscore --save-dev

This adds an entry for underscore in the devDependencies section of the bower.json...