Example of express middleware

middleware.test.js

const cache = require('./cache')
const db = require('./db')

function sessionMiddleware(req, res, next) {
  const userId = req.query.id
  const user = cache.get(userId)
  if (!user) {
    db.findUserById(userId).then((result) => {
      res.body = result
      next()
    })
  } else {
    res.body = user
  next()
  } 
}