Segment.com server side page call with Express

middleware.js

import express from 'express'
import Analytics from 'analytics-node'
import { stringify } from 'qs'

const app = express()
const analytics = new Analytics('write-key')

app.use((req, res, next) => {
  const { query, cookies, url, path, ip, host } = req

  // populate campaign object with any utm params
  const campaign = {}
  if (query.utm_content) campaign.content = query.utm_content
  if (query.utm_campaign) campaign.name = query.utm_campaign
  if (query.utm_medium) campaign.medium = query.utm_medium
  if (query.utm_source) campaign.source = query.utm_source
  if (query.utm_term) campaign.keyword = query.utm_term

  // grab userId if present
  let userId = null
  if (cookies.ajs_user_id) userId = cookies.ajs_user_id

  // if no anonymousId, send a randomly generated one
  // otherwise grab existing to include in call to segment
  let anonymousId 
  if (cookies.ajs_anonymous_id) {
    anonymousId = cookies.ajs_anonymous_id
  } else {
    anonymousId = = uuid.v4()
    res.cookie('ajs_anonymous_id', anonymousId )
  }

  const referrer = req.get('Referrer')
  const userAgent = req.get('User-Agent')

  const properties = {
    query: stringify(query)
    referrer, 
    path,
    host,
    url
    /* ++ any custom props (eg. title) */
  }

  const context = {
    campaign,
    userAgent,
    ip
  }

  // send a call to segment
  analytics.page(
    anonymousId, // either random (matching cookie) or from client
    userId, // might be null
    properties, 
    context
  )

  // proceed!
  next()
  
})