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aunakaunak
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fix(response): properly serialize Array subclasses like Bun SQL results
Fixes #1656 Problem: When returning an Array subclass (e.g., Bun SQL query results), Elysia incorrectly returned '[object Object][object Object]' instead of valid JSON. Root Cause: The response handlers (mapResponse, mapEarlyResponse, mapCompactResponse) used `response?.constructor?.name === 'Array'` to detect arrays. This check fails for Array subclasses because their constructor.name is the subclass name (e.g., 'SQLResults'), not 'Array'. The response then fell through to `new Response(response)` which implicitly calls toString(), producing '[object Object]' for each element. Solution: Added `Array.isArray(response)` check in the default case of all response mapping functions. This correctly identifies all arrays including subclasses, ensuring proper JSON serialization with the correct Content-Type header. Changes: - src/adapter/bun/handler.ts: Add Array.isArray check in mapResponse, mapEarlyResponse (both branches), and mapCompactResponse default cases - src/adapter/web-standard/handler.ts: Same changes for web standard adapter - test/response/array-subclass.test.ts: Add 10 comprehensive tests covering SQL result simulation, ORM result sets, nested data, and edge cases Testing: - All 1456 tests pass (10 new tests added) - Verified with simulated Bun SQL results that previously returned '[object Object][object Object]' now correctly return JSON
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‎src/adapter/bun/handler.ts‎

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

‎src/adapter/web-standard/handler.ts‎

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

‎test/response/array-subclass.test.ts‎

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

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