Google Analytics implementation using universal-analytics and Dialogflow

.env

TRACKING_ID="UA-XXXXXXXX-Y"

handleAction.js

// error handling is done here too

module.exports = (action) => {
  switch (action) {
    case "":
      // do something
  }
}

index.js

require("dotenv").config()  // read .env file variables to process.env
const express = require("express")
const bodyParser = require("body-parser")
const Tracker = require("./Tracker.js")
const handleAction = require("./handleAction.js")

const app = express()

app.use(bodyParser.urlencoded({ extended: true }))
app.use(bodyParser.json())

const actions = [""]  // list of actions

app.post("/", (req, res) => {
  const agent = new WebhookClient({ request: req, response: res })
  const PSID = req.body.originalDetectIntentRequest.data.sender.id
  const actionHandler = (agent) => {
    try {
      if (~actions.indexOf(agent.action)) {
        const tracker = new Tracker(PSID)  // instance tracker using PSID
        tracker.sendEvent("messages", agent.action, agent.query)
        handleAction(agent.action)
      } else if (agent.action) {
        tracker.sendEvent("errors", `unhandled action ${agent.action}`, agent.query)
      }
    } catch (err) {
      tracker.sendEvent("errors", `unhandled error`, agent.query)
    }
  }
  agent.handleRequest(actionHandler)
}

package.json

{
  "dependencies": {
    "bluebird": "^3.5.2",
    "body-parser": "^1.18.3",
    "dialogflow-fulfillment": "^0.6.1",
    "dotenv": "^6.0.0",
    "express": "^4.16.3",
    "universal-analytics": "^0.4.20"
  }
}

Tracker.js

const ua = require("universal-analytics")
const bluebird = require("bluebird")

module.exports = class Tracker {
    constructor (uid) {
        this._uid = "" + uid  // cast to string
        this._visitor = ua(process.env.TRACKING_ID, this._uid, { strictCidFormat: false })
        bluebird.promisifyAll(this._visitor)
    }

    sendEvent (category, action, label) {
        if (!this._visitor) return
        this._visitor.eventAsync(category, action, label).catch((err) => console.error(err))
    }
}