diff --git a/__tests__/application/compose.ts b/__tests__/application/compose.ts
index 7a1877606..4fb1f62a9 100644
--- a/__tests__/application/compose.ts
+++ b/__tests__/application/compose.ts
@@ -1,22 +1,23 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
+import { KoaContext } from '@/context'
 
 describe('app.compose', () => {
   it('should work with default compose ', async () => {
     const app = new Koa()
-    const calls = []
+    const calls: number[] = []
 
-    app.use((ctx, next) => {
+    app.use((_ctx: KoaContext, next) => {
       calls.push(1)
       return next().then(() => {
         calls.push(4)
       })
     })
 
-    app.use((ctx, next) => {
+    app.use((_ctx: KoaContext, next) => {
       calls.push(2)
       return next().then(() => {
         calls.push(3)
@@ -37,7 +38,7 @@ describe('app.compose', () => {
     let count = 0
     const app = new Koa({
       compose (fns) {
-        return async (ctx) => {
+        return async (ctx: KoaContext) => {
           const dispatch = async () => {
             count++
             const fn = fns.shift()
@@ -48,12 +49,12 @@ describe('app.compose', () => {
       }
     })
 
-    app.use((ctx, next) => {
+    app.use((_ctx: KoaContext, next) => {
       calls.push(1)
       next()
       calls.push(4)
     })
-    app.use((ctx, next) => {
+    app.use((_ctx: KoaContext, next) => {
       calls.push(2)
       next()
       calls.push(3)
diff --git a/__tests__/application/context.ts b/__tests__/application/context.ts
index b985a8fda..4820aad87 100644
--- a/__tests__/application/context.ts
+++ b/__tests__/application/context.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
@@ -10,7 +10,7 @@ describe('app.context', () => {
   const app2 = new Koa()
 
   it('should merge properties', () => {
-    app1.use((ctx, next) => {
+    app1.use(ctx => {
       assert.strictEqual(ctx.msg, 'hello')
       ctx.status = 204
     })
@@ -21,7 +21,7 @@ describe('app.context', () => {
   })
 
   it('should not affect the original prototype', () => {
-    app2.use((ctx, next) => {
+    app2.use(ctx => {
       assert.strictEqual(ctx.msg, undefined)
       ctx.status = 204
     })
diff --git a/__tests__/application/currentContext.ts b/__tests__/application/currentContext.ts
index c277e4783..d65189610 100644
--- a/__tests__/application/currentContext.ts
+++ b/__tests__/application/currentContext.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
@@ -18,13 +18,13 @@ describe('app.currentContext', () => {
 
     app.use(async ctx => {
       assert(ctx === app.currentContext)
-      await new Promise(resolve => {
+      await new Promise<void>(resolve => {
         setTimeout(() => {
           assert(ctx === app.currentContext)
           resolve()
         }, 1)
       })
-      await new Promise(resolve => {
+      await new Promise<void>(resolve => {
         assert(ctx === app.currentContext)
         setImmediate(() => {
           assert(ctx === app.currentContext)
@@ -68,7 +68,7 @@ describe('app.currentContext', () => {
       throw new Error('error message')
     })
 
-    const handleError = new Promise((resolve, reject) => {
+    const handleError = new Promise<void>((resolve, reject) => {
       app.on('error', (err, ctx) => {
         try {
           assert.strictEqual(err.message, 'error message')
@@ -91,8 +91,8 @@ describe('app.currentContext', () => {
       throw new Error('error message')
     })
 
-    const handleError = new Promise((resolve, reject) => {
-      app.on('error', (err, ctx) => {
+    const handleError = new Promise<void>((resolve, reject) => {
+      app.on('error', err => {
         try {
           assert.strictEqual(err.message, 'error message')
           assert.strictEqual(app.currentContext, undefined)
diff --git a/__tests__/application/index.ts b/__tests__/application/index.ts
index c16ac6dde..361772672 100644
--- a/__tests__/application/index.ts
+++ b/__tests__/application/index.ts
@@ -1,6 +1,7 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
+import CreateError from 'http-errors'
 
 import { describe, it } from '@jest/globals'
 
@@ -9,7 +10,7 @@ describe('app', () => {
   (/^v18\./.test(process.version) ? it.skip : it)('should handle socket errors', done => {
     const app = new Koa()
 
-    app.use((ctx, next) => {
+    app.use(ctx => {
       // triggers ctx.socket.writable == false
       ctx.socket.emit('error', new Error('boom'))
     })
@@ -27,7 +28,7 @@ describe('app', () => {
   it('should not .writeHead when !socket.writable', done => {
     const app = new Koa()
 
-    app.use((ctx, next) => {
+    app.use(ctx => {
       // set .writable to false
       ctx.socket.writable = false
       ctx.status = 204
@@ -79,16 +80,14 @@ describe('app', () => {
   })
 
   it('should set compose from the constructor', () => {
-    const compose = () => (ctx) => {}
+    const compose = () => () => {}
     const app = new Koa({ compose })
     assert.strictEqual(app.compose, compose)
   })
 
   it('should have a static property exporting `HttpError` from http-errors library', () => {
-    const CreateError = require('http-errors')
-
     assert.notEqual(Koa.HttpError, undefined)
     assert.deepStrictEqual(Koa.HttpError, CreateError.HttpError)
-    assert.throws(() => { throw new CreateError(500, 'test error') }, Koa.HttpError)
+    assert.throws(() => { throw CreateError(500, 'test error') }, Koa.HttpError)
   })
 })
diff --git a/__tests__/application/inspect.ts b/__tests__/application/inspect.ts
index 2feb96e36..f2c532cbf 100644
--- a/__tests__/application/inspect.ts
+++ b/__tests__/application/inspect.ts
@@ -1,6 +1,6 @@
 import util from 'node:util'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/application/onerror.ts b/__tests__/application/onerror.ts
index 819f15855..68730b698 100644
--- a/__tests__/application/onerror.ts
+++ b/__tests__/application/onerror.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
-import { describe, it } from '@jest/globals'
+import { describe, expect, it, jest } from '@jest/globals'
 
 describe('app.onerror(err)', () => {
   it('should throw an error if a non-error is given', () => {
@@ -26,7 +26,7 @@ describe('app.onerror(err)', () => {
 
   it('should do nothing if status is 404', () => {
     const app = new Koa()
-    const err = new Error()
+    const err: any = new Error()
 
     err.status = 404
 
diff --git a/__tests__/application/request.ts b/__tests__/application/request.ts
index a79460f91..a9dcd4595 100644
--- a/__tests__/application/request.ts
+++ b/__tests__/application/request.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
@@ -10,7 +10,7 @@ describe('app.request', () => {
   const app2 = new Koa()
 
   it('should merge properties', () => {
-    app1.use((ctx, next) => {
+    app1.use(ctx => {
       assert.strictEqual(ctx.request.message, 'hello')
       ctx.status = 204
     })
@@ -21,7 +21,7 @@ describe('app.request', () => {
   })
 
   it('should not affect the original prototype', () => {
-    app2.use((ctx, next) => {
+    app2.use(ctx => {
       assert.strictEqual(ctx.request.message, undefined)
       ctx.status = 204
     })
diff --git a/__tests__/application/respond.ts b/__tests__/application/respond.ts
index baea1f0ac..921813449 100644
--- a/__tests__/application/respond.ts
+++ b/__tests__/application/respond.ts
@@ -2,7 +2,7 @@ import statuses from 'statuses'
 import request from 'supertest'
 import assert from 'node:assert'
 import fs from 'node:fs'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
@@ -272,12 +272,12 @@ describe('app.respond', () => {
     it('should send the right body', () => {
       const app = new Koa()
 
-      app.use((ctx, next) => {
+      app.use(ctx => {
         const res = ctx.res
         ctx.status = 200
         res.setHeader('Content-Type', 'text/html')
         res.write('Hello')
-        return new Promise(resolve => {
+        return new Promise<void>(resolve => {
           setTimeout(() => {
             res.end('Goodbye')
             resolve()
@@ -386,6 +386,7 @@ describe('app.respond', () => {
           .expect(700)
           .expect('custom status')
 
+        // @ts-ignore
         assert.strictEqual(res.res.statusMessage, 'custom status')
       })
     })
@@ -406,6 +407,7 @@ describe('app.respond', () => {
           .expect(200)
           .expect('ok')
 
+        // @ts-ignore
         assert.strictEqual(res.res.statusMessage, 'ok')
       })
     })
@@ -764,8 +766,8 @@ describe('app.respond', () => {
       it('should expose the message', () => {
         const app = new Koa()
 
-        app.use(ctx => {
-          const err = new Error('sorry!')
+        app.use(() => {
+          const err: any = new Error('sorry!')
           err.status = 403
           err.expose = true
           throw err
@@ -781,8 +783,8 @@ describe('app.respond', () => {
       it('should respond with .status', () => {
         const app = new Koa()
 
-        app.use(ctx => {
-          const err = new Error('s3 explodes')
+        app.use(() => {
+          const err: any = new Error('s3 explodes')
           err.status = 403
           throw err
         })
diff --git a/__tests__/application/response.ts b/__tests__/application/response.ts
index 61da8f8c7..a24661ee5 100644
--- a/__tests__/application/response.ts
+++ b/__tests__/application/response.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
@@ -15,7 +15,7 @@ describe('app.response', () => {
   const app7 = new Koa()
 
   it('should merge properties', () => {
-    app1.use((ctx, next) => {
+    app1.use(ctx => {
       assert.strictEqual(ctx.response.msg, 'hello')
       ctx.status = 204
     })
@@ -26,7 +26,7 @@ describe('app.response', () => {
   })
 
   it('should not affect the original prototype', () => {
-    app2.use((ctx, next) => {
+    app2.use(ctx => {
       assert.strictEqual(ctx.response.msg, undefined)
       ctx.status = 204
     })
@@ -37,7 +37,7 @@ describe('app.response', () => {
   })
 
   it('should not include status message in body for http2', async () => {
-    app3.use((ctx, next) => {
+    app3.use(ctx => {
       ctx.req.httpVersionMajor = 2
       ctx.status = 404
     })
@@ -48,7 +48,7 @@ describe('app.response', () => {
   })
 
   it('should set ._explicitNullBody correctly', async () => {
-    app4.use((ctx, next) => {
+    app4.use(ctx => {
       ctx.body = null
       assert.strictEqual(ctx.response._explicitNullBody, true)
     })
@@ -59,7 +59,7 @@ describe('app.response', () => {
   })
 
   it('should not set ._explicitNullBody incorrectly', async () => {
-    app5.use((ctx, next) => {
+    app5.use(ctx => {
       ctx.body = undefined
       assert.strictEqual(ctx.response._explicitNullBody, undefined)
       ctx.body = ''
@@ -74,7 +74,7 @@ describe('app.response', () => {
   })
 
   it('should add Content-Length when Transfer-Encoding is not defined', () => {
-    app6.use((ctx, next) => {
+    app6.use(ctx => {
       ctx.body = 'hello world'
     })
 
@@ -85,7 +85,7 @@ describe('app.response', () => {
   })
 
   it('should not add Content-Length when Transfer-Encoding is defined', () => {
-    app7.use((ctx, next) => {
+    app7.use(ctx => {
       ctx.set('Transfer-Encoding', 'chunked')
       ctx.body = 'hello world'
       assert.strictEqual(ctx.response.get('Content-Length'), undefined)
diff --git a/__tests__/application/toJSON.ts b/__tests__/application/toJSON.ts
index e4ff3cdc3..ffd0b3e2d 100644
--- a/__tests__/application/toJSON.ts
+++ b/__tests__/application/toJSON.ts
@@ -1,5 +1,5 @@
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/application/use.ts b/__tests__/application/use.ts
index 3833abb7e..fad445af6 100644
--- a/__tests__/application/use.ts
+++ b/__tests__/application/use.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/context/cookies.ts b/__tests__/context/cookies.ts
index ff9edf7bd..3e3539d1e 100644
--- a/__tests__/context/cookies.ts
+++ b/__tests__/context/cookies.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/context/inspect.ts b/__tests__/context/inspect.ts
index 20dffdca4..504d47fef 100644
--- a/__tests__/context/inspect.ts
+++ b/__tests__/context/inspect.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert'
 import util from 'node:util'
 import createContext from '../../test-helpers/context'
-import context from '../../lib/context'
+import context from '../../src/context'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/context/onerror.ts b/__tests__/context/onerror.ts
index 1a41b609a..b65a85213 100644
--- a/__tests__/context/onerror.ts
+++ b/__tests__/context/onerror.ts
@@ -1,7 +1,7 @@
 import request from 'supertest'
 import assert from 'node:assert'
 import createContext from '../../test-helpers/context'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/context/state.ts b/__tests__/context/state.ts
index 78aa955f0..0b82753a6 100644
--- a/__tests__/context/state.ts
+++ b/__tests__/context/state.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/request/href.ts b/__tests__/request/href.ts
index 984d99c9f..6b52735ef 100644
--- a/__tests__/request/href.ts
+++ b/__tests__/request/href.ts
@@ -2,7 +2,7 @@ import Stream from 'node:stream'
 import assert from 'node:assert'
 import http from 'node:http'
 import createContext from '../../test-helpers/context'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/request/inspect.ts b/__tests__/request/inspect.ts
index 984f8f3a5..18fdfe158 100644
--- a/__tests__/request/inspect.ts
+++ b/__tests__/request/inspect.ts
@@ -4,12 +4,10 @@ import createContext from '../../test-helpers/context'
 
 import { describe, it } from '@jest/globals'
 
-const { request } = createContext
-
 describe('req.inspect()', () => {
   describe('with no request.req present', () => {
     it('should return null', () => {
-      const req = request()
+      const req = createContext.request()
       req.method = 'GET'
       delete req.req
       assert(undefined === req.inspect())
@@ -18,7 +16,7 @@ describe('req.inspect()', () => {
   })
 
   it('should return a json representation', () => {
-    const req = request()
+    const req = createContext.request()
     req.method = 'GET'
     req.url = 'example.com'
     req.header.host = 'example.com'
diff --git a/__tests__/request/ip.ts b/__tests__/request/ip.ts
index 2e926f99e..533f35a0a 100644
--- a/__tests__/request/ip.ts
+++ b/__tests__/request/ip.ts
@@ -1,6 +1,6 @@
 import Stream from 'node:stream'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 import createContext from '../../test-helpers/context'
 
 import { describe, it } from '@jest/globals'
diff --git a/__tests__/response/attachment.ts b/__tests__/response/attachment.ts
index 0b60d34ed..7f8ee5aee 100644
--- a/__tests__/response/attachment.ts
+++ b/__tests__/response/attachment.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 import createContext from '../../test-helpers/context'
 
 import { describe, it } from '@jest/globals'
diff --git a/__tests__/response/flushHeaders.ts b/__tests__/response/flushHeaders.ts
index fe0a0bcbe..dead2a8e1 100644
--- a/__tests__/response/flushHeaders.ts
+++ b/__tests__/response/flushHeaders.ts
@@ -1,7 +1,7 @@
 import request from 'supertest'
 import assert from 'node:assert'
 import http from 'node:http'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/__tests__/response/header.ts b/__tests__/response/header.ts
index 73b8c8e41..364d57318 100644
--- a/__tests__/response/header.ts
+++ b/__tests__/response/header.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 import createContext from '../../test-helpers/context'
 
 import { describe, it } from '@jest/globals'
diff --git a/__tests__/response/redirect.ts b/__tests__/response/redirect.ts
index 6377d69fa..2915fe2cb 100644
--- a/__tests__/response/redirect.ts
+++ b/__tests__/response/redirect.ts
@@ -1,6 +1,6 @@
 import request from 'supertest'
 import assert from 'node:assert'
-import Koa from '../..'
+import Koa from '../../src/application'
 import createContext from '../../test-helpers/context'
 
 import { describe, it } from '@jest/globals'
diff --git a/__tests__/response/status.ts b/__tests__/response/status.ts
index e7eb0c6e4..a33fe595a 100644
--- a/__tests__/response/status.ts
+++ b/__tests__/response/status.ts
@@ -1,7 +1,7 @@
 import assert from 'node:assert'
 import request from 'supertest'
 import statuses from 'statuses'
-import Koa from '../..'
+import Koa from '../../src/application'
 import createContext from '../../test-helpers/context'
 
 import { describe, it, beforeEach } from '@jest/globals'
@@ -47,7 +47,7 @@ describe('res.status=', () => {
         const res = createContext.response({
           httpVersionMajor: 2,
           httpVersion: '2.0'
-        })
+        } as any)
         res.status = 200
         assert(!res.res.statusMessage)
       })
diff --git a/__tests__/response/writable.ts b/__tests__/response/writable.ts
index 74506bb37..382e8b73a 100644
--- a/__tests__/response/writable.ts
+++ b/__tests__/response/writable.ts
@@ -1,6 +1,6 @@
 import assert from 'node:assert'
 import net from 'node:net'
-import Koa from '../..'
+import Koa from '../../src/application'
 
 import { describe, it } from '@jest/globals'
 
diff --git a/package-lock.json b/package-lock.json
index b62221aca..6c1c09e64 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -33,13 +33,15 @@
       "devDependencies": {
         "@jest/globals": "29.7.0",
         "@types/accepts": "^1.3.7",
+        "@types/http-errors": "^2.0.4",
+        "@types/koa-compose": "3.2.8",
         "@types/node": "^20.14.9",
+        "@types/on-finished": "^2.3.4",
         "@types/parseurl": "^1.3.3",
         "@types/statuses": "2.0.5",
         "@types/supertest": "^6.0.2",
         "esbuild": "^0.21.5",
         "esbuild-jest2": "^0.6.7",
-        "gen-esm-wrapper": "^1.0.6",
         "jest": "^29.7.0",
         "snazzy": "^9.0.0",
         "standard": "^17.1.0",
@@ -1933,18 +1935,79 @@
         "@babel/types": "^7.20.7"
       }
     },
+    "node_modules/@types/body-parser": {
+      "version": "1.19.5",
+      "resolved": "https://registry.npmjs.org/@types/body-parser/-/body-parser-1.19.5.tgz",
+      "integrity": "sha512-fB3Zu92ucau0iQ0JMCFQE7b/dv8Ot07NI3KaZIkIUNXq82k4eBAqUaneXfleGY9JWskeS9y+u0nXMyspcuQrCg==",
+      "dev": true,
+      "dependencies": {
+        "@types/connect": "*",
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/connect": {
+      "version": "3.4.38",
+      "resolved": "https://registry.npmjs.org/@types/connect/-/connect-3.4.38.tgz",
+      "integrity": "sha512-K6uROf1LD88uDQqJCktA4yzL1YYAK6NgfsI0v/mTgyPKWsX1CnJ0XPSDhViejru1GcRkLWb8RlzFYJRqGUbaug==",
+      "dev": true,
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/content-disposition": {
+      "version": "0.5.8",
+      "resolved": "https://registry.npmjs.org/@types/content-disposition/-/content-disposition-0.5.8.tgz",
+      "integrity": "sha512-QVSSvno3dE0MgO76pJhmv4Qyi/j0Yk9pBp0Y7TJ2Tlj+KCgJWY6qX7nnxCOLkZ3VYRSIk1WTxCvwUSdx6CCLdg==",
+      "dev": true
+    },
     "node_modules/@types/cookiejar": {
       "version": "2.1.5",
       "resolved": "https://registry.npmjs.org/@types/cookiejar/-/cookiejar-2.1.5.tgz",
       "integrity": "sha512-he+DHOWReW0nghN24E1WUqM0efK4kI9oTqDm6XmK8ZPe2djZ90BSNdGnIyCLzCPw7/pogPlGbzI2wHGGmi4O/Q==",
       "dev": true
     },
+    "node_modules/@types/cookies": {
+      "version": "0.9.0",
+      "resolved": "https://registry.npmjs.org/@types/cookies/-/cookies-0.9.0.tgz",
+      "integrity": "sha512-40Zk8qR147RABiQ7NQnBzWzDcjKzNrntB5BAmeGCb2p/MIyOE+4BVvc17wumsUqUw00bJYqoXFHYygQnEFh4/Q==",
+      "dev": true,
+      "dependencies": {
+        "@types/connect": "*",
+        "@types/express": "*",
+        "@types/keygrip": "*",
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/estree": {
       "version": "1.0.5",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.5.tgz",
       "integrity": "sha512-/kYRxGDLWzHOB7q+wtSUQlFrtcdUccpfy+X+9iMBpHK8QLLhx2wIPYuS5DYtR9Wa/YlZAbIovy7qVdB1Aq6Lyw==",
       "dev": true
     },
+    "node_modules/@types/express": {
+      "version": "4.17.21",
+      "resolved": "https://registry.npmjs.org/@types/express/-/express-4.17.21.tgz",
+      "integrity": "sha512-ejlPM315qwLpaQlQDTjPdsUFSc6ZsP4AN6AlWnogPjQ7CVi7PYF3YVz+CY3jE2pwYf7E/7HlDAN0rV2GxTG0HQ==",
+      "dev": true,
+      "dependencies": {
+        "@types/body-parser": "*",
+        "@types/express-serve-static-core": "^4.17.33",
+        "@types/qs": "*",
+        "@types/serve-static": "*"
+      }
+    },
+    "node_modules/@types/express-serve-static-core": {
+      "version": "4.19.5",
+      "resolved": "https://registry.npmjs.org/@types/express-serve-static-core/-/express-serve-static-core-4.19.5.tgz",
+      "integrity": "sha512-y6W03tvrACO72aijJ5uF02FRq5cgDR9lUxddQ8vyF+GvmjJQqbzDcJngEjURc+ZsG31VI3hODNZJ2URj86pzmg==",
+      "dev": true,
+      "dependencies": {
+        "@types/node": "*",
+        "@types/qs": "*",
+        "@types/range-parser": "*",
+        "@types/send": "*"
+      }
+    },
     "node_modules/@types/graceful-fs": {
       "version": "4.1.9",
       "resolved": "https://registry.npmjs.org/@types/graceful-fs/-/graceful-fs-4.1.9.tgz",
@@ -1954,6 +2017,18 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/http-assert": {
+      "version": "1.5.5",
+      "resolved": "https://registry.npmjs.org/@types/http-assert/-/http-assert-1.5.5.tgz",
+      "integrity": "sha512-4+tE/lwdAahgZT1g30Jkdm9PzFRde0xwxBNUyRsCitRvCQB90iuA2uJYdUnhnANRcqGXaWOGY4FEoxeElNAK2g==",
+      "dev": true
+    },
+    "node_modules/@types/http-errors": {
+      "version": "2.0.4",
+      "resolved": "https://registry.npmjs.org/@types/http-errors/-/http-errors-2.0.4.tgz",
+      "integrity": "sha512-D0CFMMtydbJAegzOyHjtiKPLlvnm3iTZyZRSZoLq2mRhDdmLfIWOCYPfQJ4cu2erKghU++QvjcUjp/5h7hESpA==",
+      "dev": true
+    },
     "node_modules/@types/istanbul-lib-coverage": {
       "version": "2.0.6",
       "resolved": "https://registry.npmjs.org/@types/istanbul-lib-coverage/-/istanbul-lib-coverage-2.0.6.tgz",
@@ -1984,12 +2059,49 @@
       "integrity": "sha512-dRLjCWHYg4oaA77cxO64oO+7JwCwnIzkZPdrrC71jQmQtlhM556pwKo5bUzqvZndkVbeFLIIi+9TC40JNF5hNQ==",
       "dev": true
     },
+    "node_modules/@types/keygrip": {
+      "version": "1.0.6",
+      "resolved": "https://registry.npmjs.org/@types/keygrip/-/keygrip-1.0.6.tgz",
+      "integrity": "sha512-lZuNAY9xeJt7Bx4t4dx0rYCDqGPW8RXhQZK1td7d4H6E9zYbLoOtjBvfwdTKpsyxQI/2jv+armjX/RW+ZNpXOQ==",
+      "dev": true
+    },
+    "node_modules/@types/koa": {
+      "version": "2.15.0",
+      "resolved": "https://registry.npmjs.org/@types/koa/-/koa-2.15.0.tgz",
+      "integrity": "sha512-7QFsywoE5URbuVnG3loe03QXuGajrnotr3gQkXcEBShORai23MePfFYdhz90FEtBBpkyIYQbVD+evKtloCgX3g==",
+      "dev": true,
+      "dependencies": {
+        "@types/accepts": "*",
+        "@types/content-disposition": "*",
+        "@types/cookies": "*",
+        "@types/http-assert": "*",
+        "@types/http-errors": "*",
+        "@types/keygrip": "*",
+        "@types/koa-compose": "*",
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/koa-compose": {
+      "version": "3.2.8",
+      "resolved": "https://registry.npmjs.org/@types/koa-compose/-/koa-compose-3.2.8.tgz",
+      "integrity": "sha512-4Olc63RY+MKvxMwVknCUDhRQX1pFQoBZ/lXcRLP69PQkEpze/0cr8LNqJQe5NFb/b19DWi2a5bTi2VAlQzhJuA==",
+      "dev": true,
+      "dependencies": {
+        "@types/koa": "*"
+      }
+    },
     "node_modules/@types/methods": {
       "version": "1.1.4",
       "resolved": "https://registry.npmjs.org/@types/methods/-/methods-1.1.4.tgz",
       "integrity": "sha512-ymXWVrDiCxTBE3+RIrrP533E70eA+9qu7zdWoHuOmGujkYtzf4HQF96b8nwHLqhuf4ykX61IGRIB38CC6/sImQ==",
       "dev": true
     },
+    "node_modules/@types/mime": {
+      "version": "1.3.5",
+      "resolved": "https://registry.npmjs.org/@types/mime/-/mime-1.3.5.tgz",
+      "integrity": "sha512-/pyBZWSLD2n0dcHE3hq8s8ZvcETHtEuF+3E7XVt0Ig2nvsVQXdghHVcEkIWjy9A0wKfTn97a/PSDYohKIlnP/w==",
+      "dev": true
+    },
     "node_modules/@types/node": {
       "version": "20.14.9",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-20.14.9.tgz",
@@ -1999,6 +2111,15 @@
         "undici-types": "~5.26.4"
       }
     },
+    "node_modules/@types/on-finished": {
+      "version": "2.3.4",
+      "resolved": "https://registry.npmjs.org/@types/on-finished/-/on-finished-2.3.4.tgz",
+      "integrity": "sha512-Ld4UQD3udYcKPaAWlI1EYXKhefkZcTlpqOLkQRmN3u5Ml/tUypMivUHbNH8LweP4H4FlhGGO+uBjJI1Y1dkE1g==",
+      "dev": true,
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/parseurl": {
       "version": "1.3.3",
       "resolved": "https://registry.npmjs.org/@types/parseurl/-/parseurl-1.3.3.tgz",
@@ -2008,6 +2129,39 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/qs": {
+      "version": "6.9.15",
+      "resolved": "https://registry.npmjs.org/@types/qs/-/qs-6.9.15.tgz",
+      "integrity": "sha512-uXHQKES6DQKKCLh441Xv/dwxOq1TVS3JPUMlEqoEglvlhR6Mxnlew/Xq/LRVHpLyk7iK3zODe1qYHIMltO7XGg==",
+      "dev": true
+    },
+    "node_modules/@types/range-parser": {
+      "version": "1.2.7",
+      "resolved": "https://registry.npmjs.org/@types/range-parser/-/range-parser-1.2.7.tgz",
+      "integrity": "sha512-hKormJbkJqzQGhziax5PItDUTMAM9uE2XXQmM37dyd4hVM+5aVl7oVxMVUiVQn2oCQFN/LKCZdvSM0pFRqbSmQ==",
+      "dev": true
+    },
+    "node_modules/@types/send": {
+      "version": "0.17.4",
+      "resolved": "https://registry.npmjs.org/@types/send/-/send-0.17.4.tgz",
+      "integrity": "sha512-x2EM6TJOybec7c52BX0ZspPodMsQUd5L6PRwOunVyVUhXiBSKf3AezDL8Dgvgt5o0UfKNfuA0eMLr2wLT4AiBA==",
+      "dev": true,
+      "dependencies": {
+        "@types/mime": "^1",
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/serve-static": {
+      "version": "1.15.7",
+      "resolved": "https://registry.npmjs.org/@types/serve-static/-/serve-static-1.15.7.tgz",
+      "integrity": "sha512-W8Ym+h8nhuRwaKPaDw34QUkwsGi6Rc4yYqvKFo5rm2FUEhCFbzVWrxXUxuKK8TASjWsysJY0nsmNCGhCOIsrOw==",
+      "dev": true,
+      "dependencies": {
+        "@types/http-errors": "*",
+        "@types/node": "*",
+        "@types/send": "*"
+      }
+    },
     "node_modules/@types/stack-utils": {
       "version": "2.0.3",
       "resolved": "https://registry.npmjs.org/@types/stack-utils/-/stack-utils-2.0.3.tgz",
@@ -2368,16 +2522,6 @@
       "integrity": "sha512-BSHWgDSAiKs50o2Re8ppvp3seVHXSRM44cdSsT9FfNEUUZLOGWVCsiWaRPWM1Znn+mqZ1OfVZ3z3DWEzSp7hRA==",
       "dev": true
     },
-    "node_modules/assert": {
-      "version": "1.5.0",
-      "resolved": "https://registry.npmjs.org/assert/-/assert-1.5.0.tgz",
-      "integrity": "sha512-EDsgawzwoun2CZkCgtxJbv392v4nbk9XDD06zI+kQYoBM/3RBWLlEyJARDOmhAAosBjWACEkKL6S+lIZtcAubA==",
-      "dev": true,
-      "dependencies": {
-        "object-assign": "^4.1.1",
-        "util": "0.10.3"
-      }
-    },
     "node_modules/astral-regex": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/astral-regex/-/astral-regex-2.0.0.tgz",
@@ -4380,18 +4524,6 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
-    "node_modules/gen-esm-wrapper": {
-      "version": "1.1.3",
-      "resolved": "https://registry.npmjs.org/gen-esm-wrapper/-/gen-esm-wrapper-1.1.3.tgz",
-      "integrity": "sha512-LNHZ+QpaCW/0VhABIbXn45V+P8kFvjjwuue9hbV23eOjuFVz6c0FE3z1XpLX9pSjLW7UmtCkXo5F9vhZWVs8oQ==",
-      "dev": true,
-      "dependencies": {
-        "is-valid-identifier": "^2.0.2"
-      },
-      "bin": {
-        "gen-esm-wrapper": "gen-esm-wrapper.js"
-      }
-    },
     "node_modules/gensync": {
       "version": "1.0.0-beta.2",
       "resolved": "https://registry.npmjs.org/gensync/-/gensync-1.0.0-beta.2.tgz",
@@ -5170,15 +5302,6 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
-    "node_modules/is-valid-identifier": {
-      "version": "2.0.2",
-      "resolved": "https://registry.npmjs.org/is-valid-identifier/-/is-valid-identifier-2.0.2.tgz",
-      "integrity": "sha512-mpS5EGqXOwzXtKAg6I44jIAqeBfntFLxpAth1rrKbxtKyI6LPktyDYpHBI+tHlduhhX/SF26mFXmxQu995QVqg==",
-      "dev": true,
-      "dependencies": {
-        "assert": "^1.4.1"
-      }
-    },
     "node_modules/is-weakmap": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/is-weakmap/-/is-weakmap-2.0.2.tgz",
@@ -8714,27 +8837,12 @@
         "punycode": "^2.1.0"
       }
     },
-    "node_modules/util": {
-      "version": "0.10.3",
-      "resolved": "https://registry.npmjs.org/util/-/util-0.10.3.tgz",
-      "integrity": "sha1-evsa/lCAUkZInj23/g7TeTNqwPk=",
-      "dev": true,
-      "dependencies": {
-        "inherits": "2.0.1"
-      }
-    },
     "node_modules/util-deprecate": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz",
       "integrity": "sha512-EPD5q1uXyFxJpCrLnCc1nHnq3gOa6DZBocAIiI2TaSCA7VCJ1UJDMagCzIkXNsUYfD1daK//LTEQ8xiIbrHtcw==",
       "dev": true
     },
-    "node_modules/util/node_modules/inherits": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/inherits/-/inherits-2.0.1.tgz",
-      "integrity": "sha1-sX0I0ya0Qj5Wjv9xn5GwscvfafE=",
-      "dev": true
-    },
     "node_modules/v8-compile-cache": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/v8-compile-cache/-/v8-compile-cache-2.3.0.tgz",
diff --git a/package.json b/package.json
index 65385b74a..461ee9ef3 100644
--- a/package.json
+++ b/package.json
@@ -5,14 +5,12 @@
     "tag": "experimental"
   },
   "description": "Koa web app framework",
-  "main": "lib/application.js",
+  "main": "dist/application.mjs",
   "exports": {
     ".": {
-      "require": "./lib/application.js",
-      "import": "./dist/koa.mjs"
+      "require": "./dist/application.js",
+      "import": "./dist/application.mjs"
     },
-    "./*": "./*.js",
-    "./*.js": "./*.js",
     "./package": "./package.json",
     "./package.json": "./package.json"
   },
@@ -21,7 +19,7 @@
     "lint": "standard",
     "lint:pretty": "standard | snazzy",
     "authors": "git log --format='%aN <%aE>' | sort -u > AUTHORS",
-    "build": "gen-esm-wrapper . ./dist/koa.mjs",
+    "build": "tsup",
     "prepare": "npm run build"
   },
   "repository": "koajs/koa",
@@ -39,7 +37,7 @@
     "accepts": "^1.3.8",
     "cache-content-type": "^1.0.1",
     "content-disposition": "~0.5.4",
-    "content-type": "^1.0.4",
+    "content-type": "^1.0.5",
     "cookies": "~0.9.1",
     "debug": "^4.3.5",
     "delegates": "^1.0.0",
@@ -63,9 +61,11 @@
     "@types/accepts": "^1.3.7",
     "@types/parseurl": "^1.3.3",
     "@types/statuses": "2.0.5",
+    "@types/http-errors": "^2.0.4",
+    "@types/on-finished": "^2.3.4",
+    "@types/koa-compose": "3.2.8",
     "esbuild": "^0.21.5",
     "esbuild-jest2": "^0.6.7",
-    "gen-esm-wrapper": "^1.0.6",
     "@jest/globals": "29.7.0",
     "jest": "^29.7.0",
     "snazzy": "^9.0.0",
diff --git a/lib/application.js b/src/application.ts
similarity index 69%
rename from lib/application.js
rename to src/application.ts
index bbee69067..dbd477305 100644
--- a/lib/application.js
+++ b/src/application.ts
@@ -1,75 +1,83 @@
-'use strict'
+export { HttpError } from 'http-errors'
 
-/**
- * Module dependencies.
- */
+import util from 'node:util'
+import http from 'node:http'
+import assert from 'node:assert'
+import Emitter from 'node:events'
+import Stream from 'node:stream'
+import { AsyncLocalStorage } from 'node:async_hooks'
+
+import debug from 'debug';
+import onFinished from 'on-finished'
+import compose from 'koa-compose'
+import statuses from 'statuses'
+
+import response, { type KoaResponse } from './response'
+import request, { type KoaRequest } from './request'
+import context, { type KoaContext } from './context'
+
+import { only } from './utils'
 
-const debug = require('debug')('koa:application')
-const assert = require('assert')
-const onFinished = require('on-finished')
-const response = require('./response')
-const compose = require('koa-compose')
-const context = require('./context')
-const request = require('./request')
-const statuses = require('statuses')
-const Emitter = require('events')
-const util = require('util')
-const Stream = require('stream')
-const http = require('http')
-const only = require('only')
-const { HttpError } = require('http-errors')
-
-/** @typedef {typeof import ('./context') & {
- *  app: Application
- *  req: import('http').IncomingMessage
- *  res: import('http').ServerResponse
- *  request: KoaRequest
- *  response: KoaResponse
- *  state: any
- *  originalUrl: string
- * }} Context */
-
-/** @typedef {typeof import('./request')} KoaRequest */
-
-/** @typedef {typeof import('./response')} KoaResponse */
+const httpDebug = debug('koa:application')
 
 /**
  * Expose `Application` class.
  * Inherits from `Emitter.prototype`.
  */
 
-module.exports = class Application extends Emitter {
+export type KoaOptions = {
+  /** Environment */
+  env: string;
+  /** Signed cookie keys */
+  keys: string[];
+  /** Trust proxy headers */
+  proxy: boolean;
+  /** Subdomain offset */
+  subdomainOffset: number;
+  /** Proxy IP header, defaults to X-Forwarded-For */
+  proxyIpHeader: string;
+  /** Max IPs read from proxy IP header, default to 0 (means infinity) */
+  maxIpsCount: number;
+  /** No data */
+  asyncLocalStorage: boolean;
+
+  /** Function to handle middleware composition */
+  compose(args: any): void;
+}
+
+export default class Application extends Emitter {
   /**
    * Initialize a new `Application`.
    *
    * @api public
    */
 
-  /**
-    *
-    * @param {object} [options] Application options
-    * @param {string} [options.env='development'] Environment
-    * @param {string[]} [options.keys] Signed cookie keys
-    * @param {boolean} [options.proxy] Trust proxy headers
-    * @param {number} [options.subdomainOffset] Subdomain offset
-    * @param {string} [options.proxyIpHeader] Proxy IP header, defaults to X-Forwarded-For
-    * @param {number} [options.maxIpsCount] Max IPs read from proxy IP header, default to 0 (means infinity)
-    * @param {function} [options.compose] Function to handle middleware composition
-    * @param {boolean} [options.asyncLocalStorage] Max IPs read from proxy IP header, default to 0 (means infinity)
-    *
-    */
-
-  constructor (options) {
+  public proxy: boolean;
+  public subdomainOffset: number;
+  public proxyIpHeader: string;
+  public maxIpsCount: number;
+  public env: string;
+  public keys: string[];
+  public silent: boolean;
+  public ctxStorage: AsyncLocalStorage<unknown>;
+
+  public compose: any;
+  public context: KoaContext;
+  public request: KoaRequest;
+  public response: KoaResponse;
+
+  public middleware = [];
+
+  constructor (options?: KoaOptions) {
     super()
-    options = options || {}
-    this.proxy = options.proxy || false
-    this.subdomainOffset = options.subdomainOffset || 2
-    this.proxyIpHeader = options.proxyIpHeader || 'X-Forwarded-For'
-    this.maxIpsCount = options.maxIpsCount || 0
-    this.env = options.env || process.env.NODE_ENV || 'development'
-    this.compose = options.compose || compose
-    if (options.keys) this.keys = options.keys
-    this.middleware = []
+
+    this.proxy = options?.proxy || false
+    this.subdomainOffset = options?.subdomainOffset || 2
+    this.proxyIpHeader = options?.proxyIpHeader || 'X-Forwarded-For'
+    this.maxIpsCount = options?.maxIpsCount || 0
+    this.env = options?.env || process.env.NODE_ENV || 'development'
+    this.compose = options?.compose || compose
+    if (options?.keys) this.keys = options.keys
     this.context = Object.create(context)
     this.request = Object.create(request)
     this.response = Object.create(response)
@@ -78,8 +86,7 @@ module.exports = class Application extends Emitter {
     if (util.inspect.custom) {
       this[util.inspect.custom] = this.inspect
     }
-    if (options.asyncLocalStorage) {
-      const { AsyncLocalStorage } = require('async_hooks')
+    if (options?.asyncLocalStorage) {
       assert(AsyncLocalStorage, 'Requires node 12.17.0 or higher to enable asyncLocalStorage')
       this.ctxStorage = new AsyncLocalStorage()
     }
@@ -96,7 +103,7 @@ module.exports = class Application extends Emitter {
    */
 
   listen (...args) {
-    debug('listen')
+    httpDebug('listen')
     const server = http.createServer(this.callback())
     return server.listen(...args)
   }
@@ -140,7 +147,7 @@ module.exports = class Application extends Emitter {
 
   use (fn) {
     if (typeof fn !== 'function') throw new TypeError('middleware must be a function!')
-    debug('use %s', fn._name || fn.name || '-')
+    httpDebug('use %s', fn._name || fn.name || '-')
     this.middleware.push(fn)
     return this
   }
@@ -250,6 +257,8 @@ module.exports = class Application extends Emitter {
   }
 }
 
+export type KoaApplication = typeof Application
+
 /**
  * Response helper.
  */
@@ -311,10 +320,3 @@ function respond (ctx) {
   }
   res.end(body)
 }
-
-/**
- * Make HttpError available to consumers of the library so that consumers don't
- * have a direct dependency upon `http-errors`
- */
-
-module.exports.HttpError = HttpError
diff --git a/lib/context.js b/src/context.ts
similarity index 88%
rename from lib/context.js
rename to src/context.ts
index 83b4d8f9b..a3ffd8286 100644
--- a/lib/context.js
+++ b/src/context.ts
@@ -1,15 +1,9 @@
-'use strict'
-
-/**
- * Module dependencies.
- */
-
-const util = require('util')
-const createError = require('http-errors')
-const httpAssert = require('http-assert')
-const delegate = require('delegates')
-const statuses = require('statuses')
-const Cookies = require('cookies')
+import util from 'node:util'
+import createError from 'http-errors'
+import httpAssert from 'http-assert'
+import delegate from 'delegates'
+import statuses from 'statuses'
+import Cookies from 'cookies'
 
 const COOKIES = Symbol('context#cookies')
 
@@ -17,7 +11,7 @@ const COOKIES = Symbol('context#cookies')
  * Context prototype.
  */
 
-const proto = module.exports = {
+const context = {
 
   /**
    * util.inspect() implementation, which
@@ -28,7 +22,7 @@ const proto = module.exports = {
    */
 
   inspect () {
-    if (this === proto) return this
+    if (this === context) return this
     return this.toJSON()
   },
 
@@ -179,23 +173,11 @@ const proto = module.exports = {
   }
 }
 
-/**
- * Custom inspection implementation for newer Node.js versions.
- *
- * @return {Object}
- * @api public
- */
-
-/* istanbul ignore else */
-if (util.inspect.custom) {
-  module.exports[util.inspect.custom] = module.exports.inspect
-}
-
 /**
  * Response delegation.
  */
 
-delegate(proto, 'response')
+delegate(context, 'response')
   .method('attachment')
   .method('redirect')
   .method('remove')
@@ -218,7 +200,7 @@ delegate(proto, 'response')
  * Request delegation.
  */
 
-delegate(proto, 'request')
+delegate(context, 'request')
   .method('acceptsLanguages')
   .method('acceptsEncodings')
   .method('acceptsCharsets')
@@ -248,3 +230,6 @@ delegate(proto, 'request')
   .getter('fresh')
   .getter('ips')
   .getter('ip')
+
+export type KoaContext = typeof context
+export default context
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 000000000..e69de29bb
diff --git a/lib/request.js b/src/request.ts
similarity index 94%
rename from lib/request.js
rename to src/request.ts
index 7a1a07c12..4e6b0e3c8 100644
--- a/lib/request.js
+++ b/src/request.ts
@@ -1,20 +1,14 @@
-'use strict'
+import net from 'node:net'
+import qs from 'node:querystring'
+import { URL, format } from 'node:url'
 
-/**
- * Module dependencies.
- */
+import accepts from 'accepts'
+import contentType from 'content-type'
+import parse from 'parseurl'
+import fresh from 'fresh'
+import typeis from 'type-is'
 
-const URL = require('url').URL
-const net = require('net')
-const accepts = require('accepts')
-const contentType = require('content-type')
-const stringify = require('url').format
-const parse = require('parseurl')
-const qs = require('querystring')
-const typeis = require('type-is')
-const fresh = require('fresh')
-const only = require('only')
-const util = require('util')
+import { only } from './utils'
 
 const IP = Symbol('context#ip')
 
@@ -22,7 +16,7 @@ const IP = Symbol('context#ip')
  * Prototype.
  */
 
-module.exports = {
+const request = {
 
   /**
    * Return request header.
@@ -158,7 +152,7 @@ module.exports = {
     url.pathname = path
     url.path = null
 
-    this.url = stringify(url)
+    this.url = format(url)
   },
 
   /**
@@ -208,10 +202,11 @@ module.exports = {
     const url = parse(this.req)
     if (url.search === `?${str}`) return
 
+    // @ts-ignore
     url.search = str
     url.path = null
 
-    this.url = stringify(url)
+    this.url = format(url)
   },
 
   /**
@@ -712,14 +707,5 @@ module.exports = {
   }
 }
 
-/**
- * Custom inspection implementation for newer Node.js versions.
- *
- * @return {Object}
- * @api public
- */
-
-/* istanbul ignore else */
-if (util.inspect.custom) {
-  module.exports[util.inspect.custom] = module.exports.inspect
-}
+export type KoaRequest = typeof request
+export default request
diff --git a/lib/response.js b/src/response.ts
similarity index 92%
rename from lib/response.js
rename to src/response.ts
index cbe587142..b696adda2 100644
--- a/lib/response.js
+++ b/src/response.ts
@@ -1,29 +1,24 @@
-'use strict'
-
-/**
- * Module dependencies.
- */
-
-const contentDisposition = require('content-disposition')
-const getType = require('cache-content-type')
-const onFinish = require('on-finished')
-const escape = require('escape-html')
-const typeis = require('type-is').is
-const statuses = require('statuses')
-const destroy = require('destroy')
-const assert = require('assert')
-const extname = require('path').extname
-const vary = require('vary')
-const only = require('only')
-const util = require('util')
-const encodeUrl = require('encodeurl')
-const Stream = require('stream')
+import Stream from 'node:stream'
+import assert from 'node:assert'
+import { extname } from 'node:path'
+
+import vary from 'vary'
+import typeis from 'type-is'
+import onFinished from 'on-finished'
+import statuses from 'statuses'
+import escape from 'escape-html'
+import getType from 'cache-content-type'
+import encodeUrl from 'encodeurl'
+import destroy from 'destroy'
+import contentDisposition from 'content-disposition'
+
+import { only } from './utils'
 
 /**
  * Prototype.
  */
 
-module.exports = {
+const response = {
 
   /**
    * Return the request socket.
@@ -172,7 +167,7 @@ module.exports = {
 
     // stream
     if (val instanceof Stream) {
-      onFinish(this.res, destroy.bind(null, val))
+      onFinished(this.res, destroy.bind(null, val))
       if (original !== val) {
         val.once('error', err => this.ctx.onerror(err))
         // overwriting
@@ -408,7 +403,7 @@ module.exports = {
    */
 
   is (type, ...types) {
-    return typeis(this.type, type, ...types)
+    return typeis.is(this.type, type, ...types)
   },
 
   /**
@@ -587,14 +582,5 @@ module.exports = {
   }
 }
 
-/**
- * Custom inspection implementation for node 6+.
- *
- * @return {Object}
- * @api public
- */
-
-/* istanbul ignore else */
-if (util.inspect.custom) {
-  module.exports[util.inspect.custom] = module.exports.inspect
-}
+export type KoaResponse = typeof response
+export default response
diff --git a/src/utils/index.ts b/src/utils/index.ts
new file mode 100644
index 000000000..d14f0b03d
--- /dev/null
+++ b/src/utils/index.ts
@@ -0,0 +1 @@
+export * from './only'
diff --git a/src/utils/only.ts b/src/utils/only.ts
new file mode 100644
index 000000000..497042ff8
--- /dev/null
+++ b/src/utils/only.ts
@@ -0,0 +1,10 @@
+export function only(obj: object, keys){
+  obj = obj || {};
+  if ('string' == typeof keys) keys = keys.split(/ +/);
+
+  return keys.reduce(function(ret, key){
+    if (null == obj[key]) return ret;
+    ret[key] = obj[key];
+    return ret;
+  }, {});
+};
diff --git a/test-helpers/context.ts b/test-helpers/context.ts
index f6503bce9..86b66e2a4 100644
--- a/test-helpers/context.ts
+++ b/test-helpers/context.ts
@@ -1,18 +1,30 @@
 import Stream from 'node:stream'
-import Koa from '../lib/application'
+import Koa, { type KoaApplication } from '../src/application'
+import type { IncomingMessage, ServerResponse } from 'node:http'
 
-const createContext = (req, res, app) => {
+const createContext = (req?: IncomingMessage, res?: ServerResponse, app?: KoaApplication) => {
   const socket = new Stream.Duplex()
+
   req = Object.assign({ headers: {}, socket }, Stream.Readable.prototype, req)
   res = Object.assign({ _headers: {}, socket }, Stream.Writable.prototype, res)
+  // @ts-ignore
   req.socket.remoteAddress = req.socket.remoteAddress || '127.0.0.1'
+
+  // @ts-ignore
   app = app || new Koa()
-  res.getHeader = k => res._headers[k.toLowerCase()]
-  res.setHeader = (k, v) => { res._headers[k.toLowerCase()] = v }
-  res.removeHeader = (k, v) => delete res._headers[k.toLowerCase()]
+
+  // @ts-ignore
+  res.getHeader = (k: string) => res._headers[k.toLowerCase()]
+  // @ts-ignore
+  res.setHeader = (k: string, v: string) => { res._headers[k.toLowerCase()] = v }
+  // @ts-ignore
+  res.removeHeader = (k: string) => delete res._headers[k.toLowerCase()]
+
+  // @ts-ignore
   return app.createContext(req, res)
 }
 
-module.exports = createContext
-module.exports.request = (req, res, app) => createContext(req, res, app).request
-module.exports.response = (req, res, app) => createContext(req, res, app).response
+createContext.request = (req?: IncomingMessage, res?: ServerResponse, app?: KoaApplication) => createContext(req, res, app).request
+createContext.response = (req?: IncomingMessage, res?: ServerResponse, app?: KoaApplication) => createContext(req, res, app).response
+
+export default createContext
diff --git a/tsconfig.json b/tsconfig.json
index e075f973c..315a86a86 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -11,7 +11,7 @@
     // "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. */
 
     /* Language and Environment */
-    "target": "es2016",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
+    "target": "es2022",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
     // "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
     // "jsx": "preserve",                                /* Specify what JSX code is generated. */
     // "experimentalDecorators": true,                   /* Enable experimental support for legacy experimental decorators. */
@@ -25,11 +25,13 @@
     // "moduleDetection": "auto",                        /* Control what method is used to detect module-format JS files. */
 
     /* Modules */
-    "module": "commonjs",                                /* Specify what module code is generated. */
+    "module": "NodeNext",                                /* Specify what module code is generated. */
     // "rootDir": "./",                                  /* Specify the root folder within your source files. */
     // "moduleResolution": "node10",                     /* Specify how TypeScript looks up a file from a given module specifier. */
-    // "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
-    // "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
+    "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
+    "paths": {
+      "@/*": ["src/*"]
+    },                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
     // "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */
     // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
     // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
@@ -82,7 +84,7 @@
     "forceConsistentCasingInFileNames": true,            /* Ensure that casing is correct in imports. */
 
     /* Type Checking */
-    "strict": true,                                      /* Enable all strict type-checking options. */
+    "strict": false,                                      /* Enable all strict type-checking options. */
     // "noImplicitAny": true,                            /* Enable error reporting for expressions and declarations with an implied 'any' type. */
     // "strictNullChecks": true,                         /* When type checking, take into account 'null' and 'undefined'. */
     // "strictFunctionTypes": true,                      /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */
diff --git a/tsup.config.ts b/tsup.config.ts
new file mode 100644
index 000000000..80c5505e8
--- /dev/null
+++ b/tsup.config.ts
@@ -0,0 +1,9 @@
+import { defineConfig } from 'tsup'
+
+export default defineConfig({
+  entry: ['src/application.ts'],
+  format: ['cjs', 'esm'],
+  target: 'es2022',
+  dts: true,
+  clean: true
+})