fix(response): properly serialize Array subclasses like Bun SQL results

src/adapter/bun/handler.ts

@@ -140,6 +140,12 @@ export const mapResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					set.headers['content-type'] = 'application/json'
+					return new Response(JSON.stringify(response), set as any)
+				}
+
 				return new Response(response as any, set as any)
 		}
 	}
@@ -279,6 +285,12 @@ export const mapEarlyResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					set.headers['content-type'] = 'application/json'
+					return new Response(JSON.stringify(response), set as any)
+				}
+
 				return new Response(response as any, set as any)
 		}
 	} else
@@ -397,6 +409,13 @@ export const mapEarlyResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					return new Response(JSON.stringify(response), {
+						headers: { 'content-type': 'application/json' }
+					})
+				}
+
 				return new Response(response as any)
 		}
 }
@@ -515,6 +534,13 @@ export const mapCompactResponse = (
 				}
 			}
 
+			// Handle Array subclasses (e.g., Bun SQL results)
+			if (Array.isArray(response)) {
+				return new Response(JSON.stringify(response), {
+					headers: { 'Content-Type': 'application/json' }
+				})
+			}
+
 			return new Response(response as any)
 	}
 }

src/adapter/web-standard/handler.ts

@@ -172,6 +172,12 @@ export const mapResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					set.headers['content-type'] = 'application/json'
+					return new Response(JSON.stringify(response), set as any)
+				}
+
 				return new Response(response as any, set as any)
 		}
 	}
@@ -312,6 +318,12 @@ export const mapEarlyResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					set.headers['content-type'] = 'application/json'
+					return new Response(JSON.stringify(response), set as any)
+				}
+
 				return new Response(response as any, set as any)
 		}
 	} else
@@ -431,6 +443,13 @@ export const mapEarlyResponse = (
 					}
 				}
 
+				// Handle Array subclasses (e.g., Bun SQL results)
+				if (Array.isArray(response)) {
+					return new Response(JSON.stringify(response), {
+						headers: { 'content-type': 'application/json' }
+					})
+				}
+
 				return new Response(response as any)
 		}
 }
@@ -553,6 +572,13 @@ export const mapCompactResponse = (
 				}
 			}
 
+			// Handle Array subclasses (e.g., Bun SQL results)
+			if (Array.isArray(response)) {
+				return new Response(JSON.stringify(response), {
+					headers: { 'Content-Type': 'application/json' }
+				})
+			}
+
 			return new Response(response as any)
 	}
 }

test/response/array-subclass.test.ts

@@ -0,0 +1,213 @@
+import { Elysia } from '../../src'
+import { describe, expect, it } from 'bun:test'
+import { req } from '../utils'
+
+/**
+ * Test for issue #1656: Returning non-JSON serializable response when using Elysia with Bun SQL
+ * 
+ * Problem: When returning an Array subclass (like Bun SQL results), Elysia was using
+ * constructor.name === 'Array' to detect arrays, which fails for subclasses.
+ * This caused the response to fall through to `new Response(response)` which
+ * implicitly calls toString() resulting in "[object Object][object Object]".
+ * 
+ * Fix: Use Array.isArray() to properly detect all arrays including subclasses.
+ */
+
+// Simulate Bun SQL results - an array subclass with extra properties
+class SQLResults extends Array<any> {
+	statement: string = 'SELECT * FROM users'
+	columns: string[] = ['id', 'name']
+
+	constructor(...items: any[]) {
+		super(...items)
+		Object.setPrototypeOf(this, SQLResults.prototype)
+	}
+}
+
+// Another common case: TypedArray-like results from ORMs
+class ORMResultSet extends Array<any> {
+	query: string
+	duration: number
+
+	constructor(query: string, duration: number, ...items: any[]) {
+		super(...items)
+		this.query = query
+		this.duration = duration
+		Object.setPrototypeOf(this, ORMResultSet.prototype)
+	}
+}
+
+describe('Array Subclass Response Serialization', () => {
+	describe('Issue #1656 - Bun SQL results', () => {
+		it('should serialize Array subclass (SQLResults) as JSON', async () => {
+			const app = new Elysia().get('/', () => {
+				return new SQLResults(
+					{ id: 1, name: 'Alice' },
+					{ id: 2, name: 'Bob' }
+				)
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([
+				{ id: 1, name: 'Alice' },
+				{ id: 2, name: 'Bob' }
+			])
+		})
+
+		it('should serialize Array subclass with set headers', async () => {
+			const app = new Elysia().get('/', ({ set }) => {
+				set.headers['X-Custom'] = 'test'
+				return new SQLResults({ id: 1, name: 'Alice' })
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(response.headers.get('X-Custom')).toBe('test')
+			expect(data).toEqual([{ id: 1, name: 'Alice' }])
+		})
+
+		it('should handle empty Array subclass', async () => {
+			const app = new Elysia().get('/', () => {
+				return new SQLResults()
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([])
+		})
+
+		it('should serialize ORM result sets correctly', async () => {
+			const app = new Elysia().get('/', () => {
+				return new ORMResultSet(
+					'SELECT * FROM products',
+					42,
+					{ id: 1, name: 'Widget', price: 9.99 },
+					{ id: 2, name: 'Gadget', price: 19.99 }
+				)
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([
+				{ id: 1, name: 'Widget', price: 9.99 },
+				{ id: 2, name: 'Gadget', price: 19.99 }
+			])
+		})
+	})
+
+	describe('mapEarlyResponse with Array subclass', () => {
+		it('should serialize Array subclass in beforeHandle', async () => {
+			const app = new Elysia()
+				.get('/', () => 'fallback', {
+					beforeHandle: () => {
+						return new SQLResults(
+							{ id: 1, name: 'Early' }
+						)
+					}
+				})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([{ id: 1, name: 'Early' }])
+		})
+
+		it('should serialize Array subclass in beforeHandle with set headers', async () => {
+			const app = new Elysia()
+				.get('/', ({ set }) => {
+					set.headers['X-Test'] = 'value'
+					return 'fallback'
+				}, {
+					beforeHandle: ({ set }) => {
+						set.status = 201
+						return new SQLResults({ id: 1, created: true })
+					}
+				})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.status).toBe(201)
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([{ id: 1, created: true }])
+		})
+	})
+
+	describe('Nested Array subclasses', () => {
+		it('should handle Array subclass containing nested arrays', async () => {
+			const app = new Elysia().get('/', () => {
+				return new SQLResults(
+					{ id: 1, tags: ['a', 'b', 'c'] },
+					{ id: 2, tags: ['d', 'e'] }
+				)
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(data).toEqual([
+				{ id: 1, tags: ['a', 'b', 'c'] },
+				{ id: 2, tags: ['d', 'e'] }
+			])
+		})
+
+		it('should handle Array subclass containing nested objects', async () => {
+			const app = new Elysia().get('/', () => {
+				return new SQLResults(
+					{
+						id: 1,
+						user: { name: 'Alice', email: 'alice@example.com' },
+						orders: [{ orderId: 100 }, { orderId: 101 }]
+					}
+				)
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(data).toEqual([
+				{
+					id: 1,
+					user: { name: 'Alice', email: 'alice@example.com' },
+					orders: [{ orderId: 100 }, { orderId: 101 }]
+				}
+			])
+		})
+	})
+
+	describe('Regular arrays still work', () => {
+		it('should still serialize regular arrays', async () => {
+			const app = new Elysia().get('/', () => {
+				return [{ id: 1 }, { id: 2 }]
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual([{ id: 1 }, { id: 2 }])
+		})
+
+		it('should still serialize plain objects', async () => {
+			const app = new Elysia().get('/', () => {
+				return { message: 'hello' }
+			})
+
+			const response = await app.handle(req('/'))
+			const data = await response.json()
+
+			expect(response.headers.get('content-type')).toBe('application/json')
+			expect(data).toEqual({ message: 'hello' })
+		})
+	})
+})