Modern JavaScript Web Development Cookbook

Code splitting for performance

As your application grows in size, it will progressively be slower to load, and that will be off-putting to your users. (And, remember that not everybody has access to high-speed connections, especially in mobile devices!) Furthermore, users shouldn't have to download the whole code if they only need a small part of it: for example, if a user wants to browse products, why should the sign-up view be downloaded? 

The solution to this space and speed problem is code splitting, which implies that your application will be broken down into smaller chunks that will be loaded only if needed. Fortunately, there are very good tools for this, which don't involve many changes to your existing code, so it's a win all around. ...