Explain Fast Refresh and how it superseded Hot Reload and Live Reload. What edge cases force a full reload?

Fast Refresh (RN 0.61+, 2019) is React Native's hot-update system — it preserves your component state when you save a file. It replaced both the older Hot Reload and Live Reload features.

The history (and why they're gone):

• Live Reload — reloaded the whole app on every file save; you lost all in-memory state (the screen you were on, form input, navigation stack).

• Hot Reload — tried to inject changes without re-mounting; brittle, often left the app in a desynced state.

• Fast Refresh (2019, deprecated the other two) — best of both: per-component updates with state preserved, plus a graceful fall-back to full reload when needed.

How Fast Refresh works:

• Updates React components in place; preserves their useState values.

• Recovers from syntax errors and runtime errors automatically — saving the fix re-applies cleanly.

Edge cases that force a full reload:

• Editing a non-component file (utils, helpers, services) — Fast Refresh can't safely hot-swap, so it reloads.

• Editing a class component (functional components are first-class).

• Module-level side effects (file-level console.log, top-level event listeners).

• Changes to native modules or anything outside the JS bundle (Info.plist, AppDelegate) — full rebuild required.