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To activate development mode, set development: true.
https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35bserver.ts
Bun.serve({
  development: true, 
  fetch(req) {
    throw new Error("woops!");
  },
});
In development mode, Bun surfaces errors in-browser with a built-in error page.
Bun's built-in 500 page

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error callback

To handle server-side errors, implement an error handler. Return a Response to serve to the client when an error occurs. In development mode, this response replaces Bun’s default error page. 
Bun.serve({
  fetch(req) {
    throw new Error("woops!");
  },
  error(error) {
    return new Response(`<pre>${error}\n${error.stack}</pre>`, {
      headers: {
        "Content-Type": "text/html",
      },
    });
  },
});
Learn more about debugging in Bun