Drupal 8 relies on a number of JavaScript libraries and plugins to perform some of its frontend tasks. For example, the use of Backbone.js is another example of advancement from previous versions of Drupal when it comes to adopting established libraries rather than reinventing new ones. Of course, as we already saw, the ubiquitous jQuery library continues to be used in Drupal 8 as well. But of course, there's others.
Another thing I have already mentioned but which is helpful to bring up again is the fact that Drupal no longer loads things such as jQuery or its Ajax framework on all pages needlessly. For example, many pages serving anonymous users which do not require jQuery won't even load it. This can greatly improve performance. But it also means that when we define our libraries to include our own JavaScript files, we must always declare these...
