bun-hot-reloading

Run your server with bun --hot run src/server.ts to reload modules in-place without restarting the process. For full process restarts on file changes, use bun --watch run src/index.ts instead.

The --watch flag restarts the entire process when files change, losing all in-memory state. The --hot flag reloads modules in-place, preserving state, and is designed for Bun.serve HTTP servers.

Store state on globalThis, for example globalThis.cache ??= new Map(), so it survives module reloads. Module-level variables are reset when the module is re-evaluated during a hot reload.

State is lost because you are either using --watch, which restarts the whole process, or storing state in module-level variables. Switch to --hot and move persistent state to globalThis.

Yes, run Vite through Bun with bunx --bun vite and enable hmr in the Vite server config. This gives frontend hot module replacement while Bun executes the dev server.

Register a cleanup callback with import.meta.hot.dispose() and clear intervals or close connections inside it. Without dispose handlers, old timers and sockets keep running after each reload, causing memory leaks.