cors

Kind: Function

Source: src/middleware/cors/index.ts

Part of: Middleware

CORS Middleware for Hono.

cors creates Hono middleware that adds Cross-Origin Resource Sharing headers to responses and handles browser preflight requests. Configure it at the app or route scope to control allowed origins, methods, request headers, exposed headers, and credentials.

Signature

ts
function cors(options: CORSOptions): MiddlewareHandler

Parameters

Returns: MiddlewareHandler

Diagram

mermaid
graph LR
  Request[Incoming request] --> Middleware[cors options]
  Middleware --> Check{Preflight request?}
  Check -->|Yes| Preflight[Return CORS response headers]
  Check -->|No| Next[Run downstream Hono handler]
  Next --> Response[Add CORS response headers]

Usage

ts
import { Hono } from 'hono'
import { cors } from 'hono/cors'

const app = new Hono()

app.use(
  '/api/*',
  cors({
    origin: 'https://example.com',
    allowMethods: ['GET', 'POST'],
    allowHeaders: ['Content-Type', 'Authorization'],
    credentials: true,
  })
)

app.get('/api/users', (c) => {
  return c.json({ users: [] })
})

export default app

AI Coding Instructions

• Register cors before the routes that need CORS headers, using app.use() with an appropriate path scope.
• Set a specific origin when credentials is enabled; browsers reject credentialed responses with a wildcard origin.
• Configure allowMethods and allowHeaders to match the methods and headers sent by browser clients.
• Do not add separate OPTIONS handlers for routes covered by this middleware unless custom preflight behavior is required.