🔧 fix: respect toResponse() method on Error classes

src/adapter/bun/handler.ts

@@ -526,8 +526,24 @@ 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
+		const raw = error.toResponse()
+		const targetSet =
+			set ?? ({ headers: {}, status: 200, redirect: '' } as Context['set'])
+		const apply = (resolved: unknown) => {
+			if (resolved instanceof Response) targetSet.status = resolved.status
+			return mapResponse(resolved, targetSet)
+		}
+
+		return typeof raw?.then === 'function'
+			? raw.then(apply)
+			: apply(raw)
+	}
+
+	return new Response(
 		JSON.stringify({
 			name: error?.name,
 			message: error?.message,
@@ -539,6 +555,7 @@ 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 +559,24 @@ 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
+		const raw = error.toResponse()
+		const targetSet =
+			set ?? ({ headers: {}, status: 200, redirect: '' } as Context['set'])
+		const apply = (resolved: unknown) => {
+			if (resolved instanceof Response) targetSet.status = resolved.status
+			return mapResponse(resolved, targetSet)
+		}
+
+		return typeof raw?.then === 'function'
+			? raw.then(apply)
+			: apply(raw)
+	}
+
+	return new Response(
 		JSON.stringify({
 			name: error?.name,
 			message: error?.message,
@@ -572,6 +588,7 @@ export const errorToResponse = (error: Error, set?: Context['set']) =>
 			headers: set?.headers as any
 		}
 	)
+}
 
 export const createStaticHandler = (
 	handle: unknown,

src/compose.ts

@@ -1,6 +1,6 @@
 import type { AnyElysia } from './index'
 
-import { Value } from '@sinclair/typebox/value'
+import { Value, TransformDecodeError } from '@sinclair/typebox/value'
 import {
 	Kind,
 	OptionalKind,
@@ -2520,6 +2520,8 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		`mapResponse,` +
 		`ERROR_CODE,` +
 		`ElysiaCustomStatusResponse,` +
+		`ValidationError,` +
+		`TransformDecodeError,` +
 		allocateIf(`onError,`, app.event.error) +
 		allocateIf(`afterResponse,`, app.event.afterResponse) +
 		allocateIf(`trace,`, app.event.trace) +
@@ -2529,11 +2531,8 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		adapterVariables +
 		`}=inject\n`
 
-	fnLiteral += `return ${
-		app.event.error?.find(isAsync) || app.event.mapResponse?.find(isAsync)
-			? 'async '
-			: ''
-	}function(context,error,skipGlobal){`
+	// Always make error handler async since toResponse() may return promises
+	fnLiteral += `return async function(context,error,skipGlobal){`
 
 	fnLiteral += ''
 
@@ -2598,6 +2597,17 @@ export const composeErrorHandler = (app: AnyElysia) => {
 	const saveResponse =
 		hasTrace || !!hooks.afterResponse?.length ? 'context.response = ' : ''
 
+	fnLiteral +=
+		`if(typeof error?.toResponse==='function'&&!(error instanceof ValidationError)&&!(error instanceof TransformDecodeError)){` +
+		`try{` +
+		`let raw=error.toResponse()\n` +
+		`if(typeof raw?.then==='function')raw=await raw\n` +
+		`if(raw instanceof Response)set.status=raw.status\n` +
+		`context.response=context.responseValue=raw\n` +
+		`}catch(toResponseError){\n` +
+		`}\n` +
+		`}\n`
+
 	if (app.event.error)
 		for (let i = 0; i < app.event.error.length; i++) {
 			const handler = app.event.error[i]
@@ -2606,7 +2616,7 @@ export const composeErrorHandler = (app: AnyElysia) => {
 				isAsync(handler) ? 'await ' : ''
 			}onError[${i}](context)\n`
 
-			fnLiteral += 'if(skipGlobal!==true){'
+			fnLiteral += 'if(skipGlobal!==true&&!context.response){'
 
 			if (hasReturn(handler)) {
 				fnLiteral +=
@@ -2652,17 +2662,16 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		}
 
 	fnLiteral +=
-		`if(error.constructor.name==="ValidationError"||error.constructor.name==="TransformDecodeError"){\n` +
+		`if(error instanceof ValidationError||error instanceof TransformDecodeError){\n` +
 		`if(error.error)error=error.error\n` +
 		`set.status=error.status??422\n` +
 		afterResponse() +
 		adapter.validationError +
 		`\n}\n`
 
 	fnLiteral +=
-		`if(error instanceof Error){` +
+		`if(!context.response&&error instanceof Error){` +
 		afterResponse() +
-		`\nif(typeof error.toResponse==='function')return context.response=context.responseValue=error.toResponse()\n` +
 		adapter.unknownError +
 		`\n}`
 
@@ -2710,6 +2719,8 @@ export const composeErrorHandler = (app: AnyElysia) => {
 		mapResponse: app['~adapter'].handler.mapResponse,
 		ERROR_CODE,
 		ElysiaCustomStatusResponse,
+		ValidationError,
+		TransformDecodeError,
 		onError: app.event.error?.map(mapFn),
 		afterResponse: app.event.afterResponse?.map(mapFn),
 		trace: app.event.trace?.map(mapFn),

src/dynamic-handle.ts

@@ -684,7 +684,23 @@ export const createDynamicErrorHandler = (app: AnyElysia) => {
 		const errorContext = Object.assign(context, { error, code: error.code })
 		errorContext.set = context.set
 
-		if (app.event.error)
+		// @ts-expect-error
+		if (typeof error?.toResponse === 'function' &&
+			!(error instanceof ValidationError) &&
+			!(error instanceof TransformDecodeError)) {
+			try {
+				// @ts-expect-error
+				let raw = error.toResponse()
+				if (typeof raw?.then === 'function') raw = await raw
+				if (raw instanceof Response) context.set.status = raw.status
+				context.response = raw
+			} catch (toResponseError) {
+				// If toResponse() throws, fall through to normal error handling
+				// Don't set context.response so onError hooks will run
+			}
+		}
+
+		if (!context.response && app.event.error)
 			for (let i = 0; i < app.event.error.length; i++) {
 				const hook = app.event.error[i]
 				let response = hook.fn(errorContext as any)
@@ -696,6 +712,19 @@ export const createDynamicErrorHandler = (app: AnyElysia) => {
 					))
 			}
 
+		if (context.response) {
+			if (app.event.mapResponse)
+				for (let i = 0; i < app.event.mapResponse.length; i++) {
+					const hook = app.event.mapResponse[i]
+					let response = hook.fn(errorContext as any)
+					if (response instanceof Promise) response = await response
+					if (response !== undefined && response !== null)
+						context.response = response
+				}
+
+			return mapResponse(context.response, context.set)
+		}
+
 		return new Response(
 			typeof error.cause === 'string' ? error.cause : error.message,
 			{