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To activate development mode, set development: true.
/icons/typescript.svgserver.ts
Bun.serve({
	development: true, 
	fetch(req) {
		throw new Error('woops!');
	},
});
In development mode, Bun will surface 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. This function should return a Response to serve to the client when an error occurs. This response will supersede Bun’s default error page in development mode. 
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
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