A lot of browsers out there lack some capabilities that come with ES2015. To fix that, we can augment our browser with this missing functionality by adding something called a polyfill. Aside from polyfills to leverage modern JavaScript, Angular is using a whole new way of detecting changes in the app and does so by using the zone.js library. Lastly, the Angular teams have decided to use Rxjs for handling HTTP requests. They have even taken it one step further to integrate it into a lot of things, such as dealing with forms and routing. These three things are what make up the core functionality that we need to import for our app to work.