Hot reload an HTTP server

The --hot flag runs a file with hot reloading enabled. When that file or a file it imports changes, Bun re-runs it. Bun does not watch files that no module imports, such as .env, bunfig.toml, and tsconfig.json. Restart Bun to apply a change to one of those files.

bun --hot run index.ts

Bun detects when you are running an HTTP server with Bun.serve(). It reloads your fetch handler when source files change, without restarting the bun process. This makes hot reloads nearly instantaneous.

Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello world");
  },
});