compose

Kind: Function

Source: src/compose.ts

Compose middleware functions into a single function based on koa-compose package.

compose combines middleware functions into one middleware handler using the dispatch pattern from koa-compose. Each middleware can run logic before and after await next(), allowing request handling, state changes, and cleanup to flow through the chain.

Signature

ts
function compose(middleware: [[Function, unknown], unknown][] | [[Function]][], onError: ErrorHandler<E>, onNotFound: NotFoundHandler<E>): ((context: Context, next?: Next) => Promise<Context>)

Parameters

Returns: ((context: Context, next?: Next) => Promise<Context>)

Diagram

mermaid
graph LR
  A[Composed middleware] --> B[Middleware A]
  B --> C[Middleware B]
  C --> D[Middleware C]
  D --> E[Final next handler]
  E --> D
  D --> C
  C --> B
  B --> A

Usage

ts
import { compose } from './compose'

type Context = {
  requestId?: string
  logs: string[]
}

const middleware = compose<Context>([
  async (context, next) => {
    context.logs.push('before request')
    await next()
    context.logs.push('after request')
  },
  async (context, next) => {
    context.requestId = crypto.randomUUID()
    await next()
  },
])

const context: Context = { logs: [] }

await middleware(context, async () => {
  context.logs.push(`handling ${context.requestId}`)
})

console.log(context.logs)

AI Coding Instructions

• Keep middleware signatures compatible with the composed handler: (context, next) => Promise<void>.
• Call and await next() when downstream middleware must run before post-processing logic.
• Do not call next() more than once from the same middleware invocation.
• Preserve middleware order when adding handlers; earlier middleware wraps later middleware.
• Pass a final next handler when composition must continue into code outside the middleware list.

Used by

2 references from 2 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

Imported by (2)

• some — src/middleware/combine/index.ts:38
• HonoOptions — src/hono-base.ts:46