Well, since you're reading this, let me tell you a little more about HMR. Magic is actually not such a good think in software development, so if we can demystify HMR a bit, it will probably benefits you when it comes to answer setup questions or, generally, get the most out of your HMR experience.

HMR allows patching the browser state without a full refresh making it particularly handy with libraries like React where a refresh blows away the application state. The Hot Module Replacement appendix covers the feature in detail.