server-no-mongoDB.js

const express = require('express')
const app = express()
const port = 3000

const users = [
  { id: 1, name: 'User 1'},
  { id: 2, name: 'User 2'},
  { id: 3, name: 'User 3'},
  { id: 4, name: 'User 4'},
  { id: 5, name: 'User 5'},
  { id: 6, name: 'User 6'},
  { id: 7, name: 'User 7'},
  { id: 8, name: 'User 8'},
  { id: 9, name: 'User 9'},
  { id: 10, name: 'User 10'},
]
const posts = [
  { id: 1, name: 'Post 1'},
  { id: 2, name: 'Post 2'},
  { id: 3, name: 'Post 3'},
  { id: 4, name: 'Post 4'},
  { id: 5, name: 'Post 5'},
  { id: 6, name: 'Post 6'},
  { id: 7, name: 'Post 7'},
  { id: 8, name: 'Post 8'},
  { id: 9, name: 'Post 9'},
  { id: 10, name: 'Post 10'},
]

// http://localhost:3000/users?page=1&limit=5

app.get('/posts', paginatedResults(posts), (req, res) => {
  res.json(res.paginatedResults)
})

app.get('/users', paginatedResults(users),(req, res) => {
  res.json(res.paginatedResults)
})

function paginatedResults(model){
  return (req, res, next) => {
    const page = +req.query.page
    const limit = +req.query.limit

    const startIndex = (page - 1 ) * limit
    const endIndex = (page * limit)

    const results = {}

    if (endIndex < model.length) {
      results.next = {
        page: page + 1,
        limit: limit
      }
    }
    
    if (startIndex > 0) {
      results.previous = {
        page: page - 1,
        limit: limit
      }
    }

    results.data = model.slice(startIndex, endIndex)

    res.paginatedResults = results
    // next will go into the next change of events which will be req, res in the route
    next()
  }
}

app.listen(port, () => console.log(`Example app listening on port ${port}!`))