example.js

const userRouter = new Router()
  .get('/', users.show)
  .use(userIsAdminMiddleware)
  .put('/', users.update)
  .del('/', users.destroy)

app
  .use('/users', new Router()
    .use('/:username', userRouter)
    .get('/', users.list)
    .post('/', users.create)
  )
  .use('/account', [
    (req, res, next) => {
      req.params.username = req.user.username
      next()
    },
    userRouter
  ])


// versus

app
  .get('/users/:username', users.show)
  .put('/users/:username', users.update)
  .del('/users/:username', users.destroy)
  .get('/users', users.list)
  .post('/users', users.create)
  // woooooot need to duplicate a bunch of routes
  .use('/account', () => (req, res, next) => {
    req.params.username = req.user.username
    next()
  })
  // woot, need to duplicate a bunch of stuff :(
  .get('/account', users.show)
  .put('/account', users.update)
  .del('/account', users.destroy)

.use('/account', () => (req, res, next) => { should be .use('/account', (req, res, next) => { and there are probably other typos