In Opine, to handle error, we need to create a special middleware that is able to receive four argument - error, request, response, and next objects. This middileware must be lastly used after all middlewares in the HTTP request cycle.

// main.ts

import {opine,serveStatic} from "https://deno.land/x/opine@2.2.0/mod.ts"

const app = opine()

app.use(serveStatic("public"))

import indexRouter from './routes/index.ts'
app.use('/',indexRouter)

app.use((err, req, res, next)=>{
  console.error(err.stack)
  res.setStatus(500).send('Something broke!')
})

app.listen(3000)
console.log("Opine started on port 3000")

// routes/index.ts

import {Router} from "https://deno.land/x/opine@2.2.0/mod.ts"
const indexRouter = Router()

const getDate = (req,res,next)=>{
    const date = (new Date()).toLocaleDateString('it-IT')
    req.date = date
    next()
}

indexRouter.use(getDate)

indexRouter.get('/', (req,res)=>{
    res.send(`Today is ${req.date}`)
})

indexRouter.get('/post/:id', (req,res)=>{
    res.send(`The id of the post is ${req.params.id}`)
})

export default indexRouter