Backbone.js is one of the popular open source JavaScript libraries that allows you to build dynamic front-end applications based on the MVC pattern. As the creators of Backbone.js emphasize, it is not a framework, so we can use or integrate only some of the library elements we need. Backbone.js is fast, has built-in routing support (pushState), has a very interesting collection and model system and its own simple templating system (Underscore templates). We can also easily replace the built-in template system with React.js.