TypeScript

TypeScript > Response Handlers - itty-router

These are specific to the finally stage in AutoRouter and Router. Each ResponseHandler has access to a response, a request, and any additional arguments provided to the router's .fetch() method. Override defaults using generics (see example).

Example: Generic

In this example, we create a generic pass-through (we return nothing) response-handler. In the finally stage, each handler that returns something replaces the response, and any handler that does not, runs, but does not modify the response.

import {
  ResponseHandler, 
  Router,
} from 'itty-router'

// defining a generic logger
const logger: ResponseHandler = (response, request) => { 
  console.log(
    response.status,
    request.url,
    'at',
    new Date().toLocaleString(),
  )
}

const router = Router({
  finally: [logger],
})

Example: Custom

In this example, we leverage the before stage to inject a request.start (timestamp), which we'll read later in the finally stage. While this would work fine without the custom StartRequest type (because the default IRequest is not strict), by strict typing and passing in the generic, our code in logger() is fully aware of request.start and its numeric nature.

import {
  ResponseHandler, 
  Router,
  IRequestStrict, 
} from 'itty-router'

type StartRequest = { 
  start: number
} & IRequestStrict

// upstream middleware to add a start time
const withStart: RequestHandler = (request) => {
  request.start = Date.now()
}

// downstream handler to log the difference (using generic)
const logger: ResponseHandler<StartRequest> = (response, request) => { 
  console.log(request.url, 'served in', Date.now() - request.start, 'ms')
}

const router = Router({
  before: [withStart],
  finally: [logger],
})