Counting unique visitors and bounces without cookies.

last-modified-demo-server.js

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

app.get('/ping', (req, res) => {
  const now = Date.now(),
    day = 8.64e7

  // calculate midnight today and tomorrow
  const midnight = Math.floor(now / day) * day
  const midnightDate = new Date(midnight)
  const midnightTomorrow = Math.ceil(now / day) * day

  // get the if-modified-since header or default to midnight
  const modified = req.headers['if-modified-since']
  let date = modified ? new Date(modified) : midnightDate

  // is the date less than today? set it to today
  date = date - midnightDate < 0 ? midnightDate : date

  // add 1 second to the date
  date.setSeconds(date.getSeconds() + 1)

  // calculate a visit count
  const counter = (date - new Date(midnight)) / 1000 - 1

  // set a max age
  const maxAge = Math.round((midnightTomorrow - now) / 1000)
  res.set('Cache-Control', `public, max-age=${maxAge}, no-cache`)

  // set last-modified header
  res.set('Last-Modified', date.toGMTString())

  // remove the etag
  res.set('etag', false)

  // return the count as a string
  res.send(String(counter))
})

app.listen(3001, () => console.log(`Counter launched on 3001`))

View a demo of this here 👉 https://lastmodified.normally.com/
And read more about it here: Privacy-preserving analytics: How we count unique visitors without cookies, UIDs or fingerprinting.