Hot Reload

Hot Reload is a development feature that applies code changes to a running application without restarting it, so the developer sees the result almost immediately. The related term hot module replacement, or HMR, describes the stricter version that swaps only the changed module and preserves application state, meaning a form stays filled and a modal stays open while the component behind it is updated. This shortens the edit-and-check loop from seconds to near-instant, which matters because that loop runs hundreds of times a day. Vite made fast HMR a baseline expectation for web development by serving native ES modules and rebuilding only what changed, and Next.js, Nuxt, and Turbopack build on the same idea. Flutter popularized the term outside the browser with its hot reload for mobile UI work. The pitfall is trusting it too far. State preserved across reloads can drift from what a fresh load would produce, so a bug that only appears after several hot updates may disappear on restart, and vice versa. Hot reload is also a development-time tool; production deploys still replace the running process, which is why a full refresh remains the honest final check.