🔧 fix: respect toResponse() method on Error classes

  Fixes toResponse() being ignored when custom error classes extend Error,
  and status code being overridden when errors with toResponse() are thrown.

  The errorToResponse() functions now check for toResponse() before creating
  default Error responses, and the error handler extracts status from the
  Response returned by toResponse() before passing it through mapResponse()

Author: MarcelOlsen

src/adapter/bun/handler.ts

@@ -526,8 +526,14 @@ export const mapCompactResponse = (
 	}
 }
 
-export const errorToResponse = (error: Error, set?: Context['set']) =>
-	new Response(
+export const errorToResponse = (error: Error, set?: Context['set']) => {
+	// @ts-expect-error
+	if (typeof error?.toResponse === 'function') {
+		// @ts-expect-error
+		return mapResponse(error.toResponse(), set ?? { headers: {}, status: 200, redirect: '' })
+	}
+
+	return new Response(
 		JSON.stringify({
 			name: error?.name,
 			message: error?.message,
@@ -539,6 +545,7 @@ export const errorToResponse = (error: Error, set?: Context['set']) =>
 			headers: set?.headers as any
 		}
 	)
+}
 
 export const createStaticHandler = (
 	handle: unknown,

src/adapter/web-standard/handler.ts

@@ -559,8 +559,14 @@ export const mapCompactResponse = (
 	}
 }
 
-export const errorToResponse = (error: Error, set?: Context['set']) =>
-	new Response(
+export const errorToResponse = (error: Error, set?: Context['set']) => {
+	// @ts-expect-error
+	if (typeof error?.toResponse === 'function') {
+		// @ts-expect-error
+		return mapResponse(error.toResponse(), set ?? { headers: {}, status: 200, redirect: '' })
+	}
+
+	return new Response(
 		JSON.stringify({
 			name: error?.name,
 			message: error?.message,
@@ -572,6 +578,7 @@ export const errorToResponse = (error: Error, set?: Context['set']) =>
 			headers: set?.headers as any
 		}
 	)
+}
 
 export const createStaticHandler = (
 	handle: unknown,

src/compose.ts

@@ -2598,6 +2598,17 @@ export const composeErrorHandler = (app: AnyElysia) => {
 	const saveResponse =
 		hasTrace || !!hooks.afterResponse?.length ? 'context.response = ' : ''
 
+	// Check for toResponse() first to handle errors with custom response methods
+	// This takes precedence over onError hooks, as the error defines its own response
+	// BUT exclude ValidationError and TransformDecodeError to allow proper validation error handling
+	fnLiteral +=
+		`if(typeof error?.toResponse==='function'&&error.constructor.name!=="ValidationError"&&error.constructor.name!=="TransformDecodeError"){` +
+		`const errorResponse=error.toResponse()\n` +
+		`if(errorResponse instanceof Response)set.status=errorResponse.status\n` +
+		afterResponse() +
+		`return context.response=context.responseValue=mapResponse(${saveResponse}errorResponse,set${adapter.mapResponseContext})\n` +
+		`}\n`
+
 	if (app.event.error)
 		for (let i = 0; i < app.event.error.length; i++) {
 			const handler = app.event.error[i]
@@ -2662,7 +2673,6 @@ export const composeErrorHandler = (app: AnyElysia) => {
 	fnLiteral +=
 		`if(error instanceof Error){` +
 		afterResponse() +
-		`\nif(typeof error.toResponse==='function')return context.response=context.responseValue=error.toResponse()\n` +
 		adapter.unknownError +
 		`\n}`
 

test/core/handle-error.test.ts

@@ -337,4 +337,99 @@ describe('Handle Error', () => {
 		expect(await res.text()).toBe('a')
 		expect(res.status).toBe(500)
 	})
+
+	it('handle Error with toResponse() when returned', async () => {
+		class ErrorA extends Error {
+			toResponse() {
+				return Response.json({ error: 'hello' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/A', () => {
+			return new ErrorA()
+		})
+
+		const res = await app.handle(req('/A'))
+
+		expect(await res.json()).toEqual({ error: 'hello' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle Error with toResponse() when thrown', async () => {
+		class ErrorA extends Error {
+			toResponse() {
+				return Response.json({ error: 'hello' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/A', () => {
+			throw new ErrorA()
+		})
+
+		const res = await app.handle(req('/A'))
+
+		expect(await res.json()).toEqual({ error: 'hello' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle non-Error with toResponse() when returned', async () => {
+		class ErrorB {
+			toResponse() {
+				return Response.json({ error: 'hello' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/B', () => {
+			return new ErrorB()
+		})
+
+		const res = await app.handle(req('/B'))
+
+		expect(await res.json()).toEqual({ error: 'hello' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle non-Error with toResponse() when thrown', async () => {
+		class ErrorB {
+			toResponse() {
+				return Response.json({ error: 'hello' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/B', () => {
+			throw new ErrorB()
+		})
+
+		const res = await app.handle(req('/B'))
+
+		expect(await res.json()).toEqual({ error: 'hello' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle Error with toResponse() that includes custom headers', async () => {
+		class ErrorWithHeaders extends Error {
+			toResponse() {
+				return Response.json(
+					{ error: 'custom error' },
+					{
+						status: 418,
+						headers: {
+							'X-Custom-Header': 'custom-value',
+							'Content-Type': 'application/json; charset=utf-8'
+						}
+					}
+				)
+			}
+		}
+
+		const app = new Elysia().get('/', () => {
+			throw new ErrorWithHeaders()
+		})
+
+		const res = await app.handle(req('/'))
+
+		expect(await res.json()).toEqual({ error: 'custom error' })
+		expect(res.status).toBe(418)
+		expect(res.headers.get('X-Custom-Header')).toBe('custom-value')
+	})
 })