When I started the myLibrary project, I invest some of my time to try and analyze a few choices out there on Internet to put on the Front-End and Back-End. Then AngularJS, an excellent choice as Front-End and ExpressJS working as Back-End.
But down the road, I found that either AngularJS and ExpressJS offer REST functionality. So, which one to use to talk to MongoDB? I could have used only AngularJS with its $http service to get data from the database, but I have decided to maintain independent the Front-End of Back-End. Development and experience aspects!