App - Hono

Hono is the primary object. It will be imported first and used until the end.

import { Hono } from 'hono'

const app = new Hono()
//...

export default app // for Cloudflare Workers or Bun

Methods

An instance of Hono has the following methods.

• app.HTTP_METHOD([path,]handler|middleware...)
• app.all([path,]handler|middleware...)
• app.on(method|method[], path|path[], handler|middleware...)
• app.use([path,]middleware)
• app.route(path, [app])
• app.basePath(path)
• app.notFound(handler)
• app.onError(err, handler)
• app.mount(path, anotherApp)
• app.fire()
• app.fetch(request, env, event)
• app.request(path, options)

The first part of them is used for routing, please refer to the routing section.

Not Found

app.notFound allows you to customize a Not Found Response.

app.notFound((c) => {
  return c.text('Custom 404 Message', 404)
})

WARNING

The notFound method is only called from the top-level app. For more information, see this issue.

Error Handling

app.onError allows you to handle uncaught errors and return a custom Response.

app.onError((err, c) => {
  console.error(`${err}`)
  return c.text('Custom Error Message', 500)
})

INFO

If both a parent app and its routes have onError handlers, the route-level handlers get priority.

fire()

WARNING

app.fire() is deprecated. Use fire() from hono/service-worker instead. See the Service Worker documentation for details.

app.fire() automatically adds a global fetch event listener.

This can be useful for environments that adhere to the Service Worker API, such as non-ES module Cloudflare Workers.

app.fire() executes the following for you:

addEventListener('fetch', (event: FetchEventLike): void => {
  event.respondWith(this.dispatch(...))
})

fetch()

app.fetch will be entry point of your application.

For Cloudflare Workers, you can use the following:

export default {
  fetch(request: Request, env: Env, ctx: ExecutionContext) {
    return app.fetch(request, env, ctx)
  },
}

or just do:

export default app

Bun:

export default app 
export default {  
  port: 3000, 
  fetch: app.fetch, 
} 

request()

request is a useful method for testing.

You can pass a URL or pathname to send a GET request. app will return a Response object.

test('GET /hello is ok', async () => {
  const res = await app.request('/hello')
  expect(res.status).toBe(200)
})

You can also pass a Request object:

test('POST /message is ok', async () => {
  const req = new Request('Hello!', {
    method: 'POST',
  })
  const res = await app.request(req)
  expect(res.status).toBe(201)
})

mount()

The mount() allows you to mount applications built with other frameworks into your Hono application.

import { Router as IttyRouter } from 'itty-router'
import { Hono } from 'hono'

// Create itty-router application
const ittyRouter = IttyRouter()

// Handle `GET /itty-router/hello`
ittyRouter.get('/hello', () => new Response('Hello from itty-router'))

// Hono application
const app = new Hono()

// Mount!
app.mount('/itty-router', ittyRouter.handle)

strict mode

Strict mode defaults to true and distinguishes the following routes.

• /hello
• /hello/

app.get('/hello') will not match GET /hello/.

By setting strict mode to false, both paths will be treated equally.

const app = new Hono({ strict: false })

router option

The router option specifies which router to use. The default router is SmartRouter. If you want to use RegExpRouter, pass it to a new Hono instance:

import { RegExpRouter } from 'hono/router/reg-exp-router'

const app = new Hono({ router: new RegExpRouter() })

Generics

You can pass Generics to specify the types of Cloudflare Workers Bindings and variables used in c.set/c.get.

type Bindings = {
  TOKEN: string
}

type Variables = {
  user: User
}

const app = new Hono<{
  Bindings: Bindings
  Variables: Variables
}>()

app.use('/auth/*', async (c, next) => {
  const token = c.env.TOKEN // token is `string`
  // ...
  c.set('user', user) // user should be `User`
  await next()
})