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Ziga Brencic
Ziga Brencic

Posted on • Originally published at

Analytics with vanilla JS: page views

How to get basic page view statistics?

Second article in the series Analytics with Vanilla JS. Motivation here.

Today we'll look into the impelentation of vanila JS analytics tool that analyses page views.

For the sake of example we need some simple HTML code for our tracker (file example_page.html). You can add anything you want to the HTML file:

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <script src="js/page_view_tracker.js"></script>
    <a href="" class="external">Leave page by going to Google</a>

The rest of the code will be in page_view_tracker.js. First, let's define the function that will allow us to POST all the gathered data as a string to a specific URL:

function post_data(data, url) {
    let xhr = new XMLHttpRequest();"POST", url, true);
    xhr.setRequestHeader("Content-Type", "application/json");
    xhr.onreadystatechange = function () {
        if (xhr.readyState === 4 && xhr.status === 200) {

data in the string is in JSON format. The server you'll be sending data to can be whatever you prefer: node.js, Django, flask, ... There's even an option to post into Google Docs spreadsheets if you want to avoid the backend.

Data is posted with the following command:

post_data(JSON.stringify(data), "");

where we defined data object as:

const data = {
    "current_page_name": current_page_name

Now let's add the rest of the data.


Number of views per page: this one is easy. Every time a user visits our website, the post_data function will be triggered, so we need to add current_page_name to our data object. It's defined with:

let current_page_name = window.location.href;

In principle, we could get the URL of the current page from the request on the backend by I prefer to have all the data in the JSON object.

User origin: We want to know from what website the user came from. This information is important because it allows us to track sources of our web site traffic. Are we getting:

  • direct traffic (users entering the URL to browser),
  • traffic via referrals (links to our site), or
  • via organic search (user finds us via a Search engine like Google, Bing, Baidu ...).

In all browsers except the Internet Explorer, the following will give us the source from which user came:

let page_source = document.referrer;

If traffic is dirrect or user used Internet Explorer page_source will be empty so we set:

if (page_source === "") {
    // could be direct traffic or Internet explorer
    page_source = "empty";

Now we can detect what web browser the user has with something like this, but that doesn't help us to determine the source from which the user came. If you know a workaround, please let me know how to get user origin in IE.

Device screen: We want to know what devices the majority of our users are using. We get device screen size via:

let screen_width = window.screen.width;
let screen_height = window.screen.height;

and screen size that we can draw on with:

let screen_available_width = window.screen.availWidth;
let screen_available_height = window.screen.availHeight;

Browser type, language, time zone: To get the browser type we do:

let browser_type = navigator.userAgent;

the language:

let language = navigator.language;

and the time zone:

let time_zone_offset = Intl.DateTimeFormat().resolvedOptions().timeZone;

Tracking parameters: You can enhance your analytics if you publish URL-s with added parameters. For example, you can use the Urchin Tracking Module or UTM, a format used by Google to track your unique URLs:

By adding parameters to links you share, you can segment the traffic way better during the analysis process. For example: What was published by you, what was shared by others, social media source, ...

Page performance: We want to know how long does it take for our web page to load. For that, we need to understand a bit about web browser events:

Alt Text

  • 1.) First, the browser sends the request to the server to get page files.
  • 2.) Page files are sent to our device.
  • 3.) Then the browser needs to render the web page.
  • 4.) Once the web page is rendered, onload/load event is triggered.
  • 5.) The user views the page.
  • 6.) The onload/onunload event happens when the user closes the web page.

The page loading and rendering should happen in a matter of ms. If it doesn't, our user either has a really crapy internet, or we are sending over to many files. Either way, it's good to track that. According to Mozilla docs we can obtain the data about page loading from:

let performance_data = window.performance.timing;

Then get:

let page_load_time = performance_data.loadEventEnd - performance_data.navigationStart;
let request_response_time = performance_data.responseEnd - performance_data.requestStart;
let render_time = performance_data.domComplete - performance_data.domLoading;

We need to trigger page performance monitoring code after the page is loaded. Full code snipet for page perfromance:

window.addEventListener("load", function () {
    let performance_data = window.performance.timing;

    // calculate request response time: network latency
    let request_response_time = ...

    // calculate page render time
    let render_time = ...

    // page load time: wait until load event is finished with setTimeout
    setTimeout(function () {
        let page_load_time = ...

        // Post data to the server
    }, 0);

setTimeOut is needed because we need to wait for the load event to finish before we can measure the page load time.

Stay tuned

The full code can be found on my blog at page views. There you'll find the HTML, JS, python files you need to run the whole thing.

If you have any ideas what else we could track or how let me know in the comment section below.

I'm not a very proficient JavaScript developer, so there is probably a better way to do some of the parts. Any comments and solutions are welcome. Stay tuned for more. Next week we'll look into page view duration tracking. Why an entire article for that? Well, there are a few edge cases with web page closing that can complicate things.

Top comments (18)

byrro profile image
Renato Byrro

That's an interesting exercise, looking forward to the next posts.

I think what's essential is not amount of data, but just the necessary and right datapoints that answer the right questions. I feel Google Analytics is bloated, difficult to use, it's like "Microsoft Office" of web analytics. We only need a text editor with markdown.

I'd focus more on which data and how to present, instead of too much on collecting everything possible...

zigabrencic profile image
Ziga Brencic

Hey 👋 couldn’t agree more one the analogy you made. Might use it in the future 😉

Speaking of simplicity. What would you focus on collecting and visualizing? I have few things in mind but I’m open to suggestions where to take the above series 🙂 Let me now.

byrro profile image
Renato Byrro • Edited

In my (relatively short) experience:

It doesn't hurt to have aggregate metrics like time series of sessions, pageviews, geographical distribution of users, etc. I think what's challenging is making it easier (in the UI) to draw answers to simple questions:

  • In what countries is the site most popular, which topics are more interesting to each country?
  • Which source brings the best traffic (perhaps people that spent more time on the site, on average)?

But the bottom line is: almost always we want people to take certain "actions" - subscribe to newsletter, buy stuff, start a Trial account, etc.

What I think people really need is to connect sources and efforts to actions.

An "effort" is: "I publish an article about a service I think is valuable to other devs". Or "I post on social media about a new feature or a case study of this service".

A source could be DEVto, in case of article, or Twitter in case of the post.

Even if the person comes in today, but only take the "action" 3 weeks later, I would like to know which "efforts" contributed. There are automation marketing platforms that would give that, but (again) they are so bloated that you need "marketing specialists" to configure them correctly. Not to mention how expensive they are. It's ridiculous, should be really simple and cheap for individuals, SMEs and startups.

Side note: it's become common sense for developers to demonize marketing; although I understand there are unacceptable abuses nowadays, I find amazing to see the rationale of someone who takes a 6-figure salary from a company (which in some cases is the largest privacy abusers) that must connect to a market that can benefit from its service (a.k.a. Marketing) in order to keep money flowing in to pay for fat salaries every month. And then this person despise who works in marketing, analytics, etc. It's amazing...

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zigabrencic profile image
Ziga Brencic

Hey thanks for this.

As I mentioned in the first article of the series Motivation I'm going towards analytics that can be integrated directly into product development cycle. What you described definitely fits the bill. Really good point if you don't mind I'll use it :)

On marketing <=> developer relationships I couldn't agree more. Software is useless if nobody's using it and developers are too often way to far from direct customer interaction.

If you ask me. Software development is easy. Selling the product is hard :D

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byrro profile image
Renato Byrro • Edited

Sure, feel free to use the ideas! Glad I could add something positive to the discussion! Please, keep us posted as you move forward 😉

I couldn't agree more: software is not an obstacle, being able to sell profitably and grow healthy is really hard!

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zigabrencic profile image
Ziga Brencic

Great. I want to bounce another thought.

Tracking sources of traffic is easy. Proper URL parameters and that's it. But connecting efforts to actions over multiple web page user visits that's a bit harder.

I've come up with a solution that uses localStorage but local storage can disabled. Sure the amount of users with disabled localStorage will be small but still.

Is there maybe a more elegant way to connect multiple separate web page visits to a single user? I'm probably missing something due to my basic knowledge of JS.

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byrro profile image
Renato Byrro • Edited

I would suggest generating a unique hash for each visitor. Maybe an MD5 hash of multiple values concatenated:

  • User-agent
  • IP address
  • Timestamp
  • Random 9-digit number (extra careful avoiding hash collision)

Store this hash as a cookie in the browser. When the person comes back later, your script can identify it's the same person.

Store the user hash with every interaction (even pageviews). Later, when you're analyzing an action (e.g. "user subscribed to the service"), you can get the user-hash and search every other interaction associated with it in the past.

About tracking the source of traffic, it's not going to be easy anymore. All major browsers are adopting strict "no-referrer" policies now. What this means is:

  1. The person is reading an article in
  2. There's a link to your site (, in which the reader clicks
  3. When requesting your site content, the browser will send only "" in the Referrer Header, not the entire URL

They're making this switch for privacy and security reasons. It's a good thing, but it will make it a lot more difficult to track sources with precision. Unless we use UTM parameters in the URL, there's no way to know from which page the visitor came.

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zigabrencic profile image
Ziga Brencic • Edited

Hash thats clever 🙂 I was thinking about just some unique user id. Thanks.

On URL. Privacy reasons I get and I know that UTMs are more reliable but what are the security issues of referrals?

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byrro profile image
Renato Byrro

It's possible for the origin to add user sensitive data in the URL. It's bad practice, but I'd say there's 99.99999% chance that at least a handful of sites is doing that right now.

In that event, the target site can access user data without its consent from the referrer header.

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zigabrencic profile image
Ziga Brencic

Alright yeah that’s problematic. Never thought of that 🤷‍♂️

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byrro profile image
Renato Byrro

Me neither!.. 😊

I was just pissed at Google Analytics recently and thinking about building something better and started researching, your article caught my attention 😄

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zigabrencic profile image
Ziga Brencic

Haha nice :D

My disagreement with Google Analytics got on this path to yeah. What encouraged me to start building my own analytics were those guys:

Before that I never thought that one could build reliable custom analytics. But apparently two developers did.

sidvishnoi profile image
Sid Vishnoi

As an improvement, have a look at the Fetch API and Beacon API 🙂

zigabrencic profile image
Ziga Brencic

Thanks for pointing that out.

I didn't know about Fetch and Beacon API. Though after a quick google search I noticed that they are not supported in IE. At least according to

Any thoughts how to perform asynchronous requests in IE?

It would be a performance improvement indeed.

sidvishnoi profile image
Sid Vishnoi

I would recommend not supporting IE anymore, unless absolutely needed. You can always fall back to XHR if fetch is not available (polyfill).

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zigabrencic profile image
Ziga Brencic

IE is still supported and developed right? What am I missing here?

I checked my personal page and yes percentage of IE users is low but still. Fall back to XHR sounds like a good option.

How would you do the fall back? With try and catch? Or would you try to detect if user is on IE? If yes how? As far as I know there's no consistent way to check browser version.

As I mentioned in the article I'm a bit light on JS since I come from data science. So any tips are welcome :)

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sidvishnoi profile image
Sid Vishnoi • Edited

IE 11 is still supported by Microsoft, but not for long. Adding a development focus on IE in 2019 is a waste of efforts, unless it's absolutely necessary. You can do it in a progressive way, where a site is usable on IE, but won't support all the features.

Falling back to XHR can be as simple as checking if (!window.fetch).

There used to be some specific HTML comments for detecting if browser is IE (not supported in IE 11). But feature detection is a better alternative than browser detection.

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zigabrencic profile image
Ziga Brencic

Alright didn't know that. Feature detection there is then.

Thanks again.