Most open source JavaScript libraries are located inside the wp-includes/js folder of your WordPress installation. Let's take a look at the following screenshot for JavaScript libraries available with WordPress 4.7:
As you can see, there are a large number of built-in libraries inside the wp-includes/js folder. WordPress uses jQuery for most of its core features, and hence, there is a separate folder for jQuery-related libraries, for example, jQuery UI, Masonry, jQuery Form plugin, and many more. Developers can use all of these libraries inside their own plugins and themes without duplicating the files. Backbone.js and Underscore.js are the latest additions to the WordPress core. These two libraries are becoming highly popular among web developers for building modularized client-side code for large-scale applications. WordPress integration with Backbone...
