Responsiveness, from the user's perspective, is a strong indicator of quality. Unresponsive user interfaces are frustrating to work with, and are unlikely to require any further scaling efforts on our part. The initial load of the application is the first impression the user has of our application, and it's also the most difficult to make fast. We looked at the challenges of loading all our resources into the browser. This is a combination of modules, dependencies, and build tools.

The next major hurdle to responsiveness in JavaScript applications are the inter-component communication bottlenecks. These usually result from too much indirection, and the design of the events required to fulfill a given feature. The components themselves can also serve as bottlenecks to responsiveness, because JavaScript is single-threaded. We went over several potential issues in this space, including the cost of maintaining state, and the cost of dealing with side effects.

The API data is what the user...