Determine how long a visitor is on a page.

December 31, 2018

Do you want to know how long a user has spent on your website? Here's how!

The Data

For each page a user visits, you'll need to store the following data:

  • user_id: a way to uniquely identify your user
  • page: the page the user visited; for example /index.html
  • opened_at: the time the user opened the page
  • last_checkin: the last time we recorded the user on that page

The Process

We're going to have two major actions:

  1. When the user first visits the page, we'll execute some Javascript to create a new data point on the server.
  2. At some regular interval (let's say every 10 seconds), we'll update the last_checkin data on the server.

The Endpoints

Let's assume that we're using the REST endpoint /data. We'll have POST /data to create a new datapoint and PUT /data/:id to update the last_checkin of that datapoint.

Of course, you would need to build this route on your server yourself, and store the data that is sent to it. Perhaps a subsequent blog post will cover how that can be achieved.

The Javascript

In the pages you want to track, you can include the following Javascript. The example uses fetch, which you will need to polyfill for full browser compatibility.

(function () {
    var checkInInterval = 10000; // check in every 10 seconds
    var userId = 1; // you'll need to figure out how you get the user id
    var data = {
        user_id: userId, 
        page: window.location.pathname,

    // create a new datapoint on the server
    fetch('/data', {
        headers: {
            'Content-Type': 'application/json',
            'Accept': 'application/json'
        method: 'POST',
        body: JSON.stringify(data)
    }).then(function (res) { return res.json() }).then(function (data) {
        setInterval(function () {

            // check in
            data.last_checkin =;
            fetch('/data/' +, {
                headers: {
                    'Content-Type': 'application/json',
                    'Accept': 'application/json'
                method: 'PUT',
                body: JSON.stringify(data)

        }, checkInInterval);

Hope this helps with your tracking needs! Of course, the easier shortcut is to use something like Google Analytics which will do it out of the box for you.