JavaScript for
Google Tag Manager

Learn JavaScript with practical examples and exercises.
Enhance your Google Tag Manager capabilities.

Level: Advanced Google Tag Manager, Beginner JavaScript
Duration: 14 hours
Last update: April 10th, 2025

In this course, you will learn:

• JavaScript essentials for advanced work with Google Tag Manager
• How to write code, use it in Custom HTML tags and Custom JS variables
• How to manipulate different data structures (e.g., adapt custom data to GA4 ecommerce tracking)
• How to adapt the data layer to different vendors
• How to write custom event listeners
• How to work with the DOM (Document Object Model) and scrape it
• Other useful use cases of JavaScript in Google Tag Manager

JavaScript is a core technology of the web. Google Tag Manager, GA4, and other web analytics tools rely on it.

GTM allows you to do many things without writing code. The user interface is friendly; you can track various interactions and send data to other vendors just by clicking buttons.

However, sometimes, things get more complicated and require advanced solutions (or cooperation with developers). I still believe that cooperation with developers is key to a robust setup. But sometimes (if you knew JavaScript), you could solve the challenges faster. By yourself.

The goal of this course is to give you enough JavaScript knowledge to solve more situations independently.

By knowing JavaScript, you will:

• be able to adapt data layer to multiple vendors
• troubleshoot your GTM setups more thoroughly
• implement advanced configurations faster and save time
• come up with solutions to more complex web tracking problems

I believe that developers are still necessary in some web-tracking situations. But if you know JavaScript, the number of such situations will go down.

Even though you can already find courses that will teach you JS, I spotted several problems:

1. Generic JavaScript courses focus on developers who build websites and apps. Not Google Tag Manager. After completing them, you will struggle with applying that specific knowledge in GTM (because of various nuances). More time will be wasted.
2. Sure, there are JavaScript courses related to GTM. But even they have problems:
   • Some courses require you to already have JS fundamentals (meaning that you must complete more courses)
   • Others might give you fundamentals, but the learning process is flawed. First, you will be bombarded with hours of theory. By the time you start applying it in GTM, you will already have forgotten half of what you learned before. Plus, they lack exercise.

What’s my solution? Read below 👇

The course structure works like this: you learn several new things in JavaScript, and then (while your learnings are fresh) I show you how to apply them in GTM. Then you learn a few more things, and then you apply them in GTM.

Rinse and repeat. That way, you will learn the topics better (and faster).

Almost every module in this course ends with two key sections:

• “How to apply new learnings in GTM”
• “Exercise” where I give you a task, you complete it and then you can compare it to my solution.

Even if you complete just the first few modules, your GTM skills will already improve. And we start from the very basics, which means that you don’t need any prior JavaScript knowledge before taking this course.

This sounds like a very low bar for an online course, right? But apparently, many Google Tag Manager courses in the market struggle with that.

If you found a course bundle or an extensive training program (that looks like a good deal), check when was the last time they updated their GTM course(s). You might be surprised 🙂

Things are different at Analytics Mania. This course is:

• Regularly updated
• Filled with practical lessons + you will apply them on a sandbox website
• Enriched with exercises where you can practice JS and learn it even better
• With easy-to-understand explanations of complex concepts
• With a clear step-by-step process (not just filled with random tutorials)
• With support from the instructor and his team
• With lifetime access (no deadlines and expiration dates)
• Taught by one of the top GTM practitioners in the world

This course is pre-recorded, which means that you are in charge of your learning schedule.

Using AI can be a huge time saver in our work. Even in this course, I share tips on how to use ChatGPT in certain situations.

But here’s the thing: AI hallucinates. AI can make up things that do not exist. There are many articles about that:

You should not blindly trust everything it says. You should verify. But how can you verify AI-generated code if you don’t know how to write code?

I am NOT saying that you must become a JavaScript expert. I am saying that you should know JS well enough to read code snippets, verify them, and, if needed, modify them.

I google code examples and use AI. Many developers do that, too. But when I find some code, I know how to modify and adapt it to my needs. After this course, you will, too.

“5-stars would be an understatement of how great this course is! The real-life practical examples are super helpful in applying what you just learned right away to small projects. You don’t have to finish the entire course before you can reap any benefits. Julius’s ability to explain abstract concepts with a true beginner’s perspective is uncanny. I have tried so many online JS courses for years, and none have ever explained things in a way people could understand like Julius does (and in far less time!). Well thought out, well-paced, and well structured–so worth it!”

– Valery Chen, Front-End Developer at The Frick Collection

100+ bite-sized videos that will show you a clear step-by-step process to learn JavaScript for Google Tag Manager as soon as possible and make the best out of it.

The only way to learn JavaScript is to actively practice. The course contains many practical examples. Also, in some lessons, you will have to complete tasks yourself (on a sandbox website).

Got questions? You will get the answers. Enroll now, and you will get multiple options on how to get help. You can join the private Facebook group of my students. Also, there is a comment section under each lesson where we can discuss.

At the end of every module, there is a quiz to check what you have learned. It’s a great way to strengthen your new knowledge. Also, most of the modules contain exercises: I give you a task to write a code, and (after you complete it) I show you my solution so that you can compare and learn.

Your “JavaScript for Google Tag Manager” course purchase includes lifetime access to the training materials. If you want to revisit a particular topic of the course, you can come back here anytime. Also, every time the course is updated, all students get that for free.

If you complete this course and still don’t understand JS well enough, email me for a refund. No questions asked.

This course is for those who are experienced Google Tag Manager users and want to take their skills to the next level. You should enroll if:

• You want to solve complex challenges with JavaScript
• You want to learn how to traverse and scrape the DOM (document object model)
• You want to adapt data layers to the custom requirements of analytics/marketing vendors
• Create custom event tracking solutions (e.g., fetch form field data if it’s not available by default)

This course is NOT for you if:

• You are a Google Tag Manager beginner or have no GTM skills at all
• You already know JavaScript pretty well
• Your main goal is to learn how to write custom templates in GTM (in this course, we focus on Custom HTML tags and Custom JS variables)

Also, you should know the fundamentals of HTML, CSS selectors, and Data Layer (what it is, what is dataLayer.push, what are Data Layer variables).

This course is on-demand. You can learn at your own pace and apply new knowledge to your own Google Tag Manager projects. Access 24/7.

“I was a complete beginner in Javascript, so this course was exactly what I was looking for. It’s challenging, but I didn’t feel overwhelmed. Julius starts with the fundamentals and slowly builds to advanced topics/use cases.

For each module, there is one or two exercises where you can practice what you learned. I’ve already been using the course content to build Custom Javascript Variables for some of my clients needs.

I’m much more confident when I talk with developers, and even though I know that it’ll take months to be proficient with Javascript, I’m ready to take on advanced tracking projects that I couldn’t tackle before.

Highly recommended if you want to step up as a web analyst / technical marketer.”

– Hugo Bruyère, Freelance Consultant of Tracking & Analytics

Julius Fedorovicius is the founder of Analytics Mania and GTM/GA4 communities on Facebook. Also, he is one of the top Google Tag Manager / Google Analytics 4 practitioners in the world.

Julius has been actively publishing articles on analyticsmania.com, a blog that helps hundreds of thousands of marketers/analysts every month and that has been featured on widely known websites like moz.com, neilpatel.com, the official Google Analytics social media accounts, etc.

Here is the list of topics that you will learn in this course. Lessons are practical and you will practice some lessons on a sandbox website (that the course provides).

Have a question? Feel free to ask!

Let’s start with the basics (before we dive into the good stuff). Topics covered:

• What is JavaScript and how it can be added to websites
• ES5 vs ES6 (how does this affect you)
• Getting familiar with JavaScript console

Now, it’s time to write your first code. We’ll look at the syntax (rules) and how to manipulate basic data (e.g., extract a particular value from text). Topics covered:

• Syntax essentials
• Variables, data types, operators
• Working with text and numbers
• Formatting data, manipulating strings and numbers
• How to apply this new knowledge in Google Tag Manager
• At the end of the module, there is an exercise that you will have to complete yourself (and then compare it to my solution). You’ll be practicing in this course a lot.

Let’s add some logic to your code. We’ll improve our codes with things like IF statements. Your code will behave depending on the conditions you define. Topics covered:

• Comparison and logical operators
• IF statement, switch, ternary operator
• How various data types behave in a boolean (true/false) context
• How to apply this new knowledge in Google Tag Manager
• As always, at the end of this module, you’ll write your own code as an exercise.

It’s time to work on more complex data structures and more serious challenges. This is where you will start feeling the of knowing JavaScript. Topics covered:

• What are arrays, objects
• How to create and manipulate arrays & objects
• Loops
• How to customize custom data layer according to vendor’s requirements (e.g., we’ll adapt custom data to GA4 ecommerce documentation)
• How to apply this new knowledge in Google Tag Manager
• This module contains multiple exercises because arrays, objects, and loops are essential topics.

Time to add more ingredients to your JavaScript stack. Topics covered:

• Functions
• Powerful array methods, such as .map()
• Scope
• How to apply this knowledge in Google Tag Manager
• Practical tasks/exercises

JS knowledge is useful not only to manipulate the data (e.g., from the data layer). It can also be used to interact with website elements. Topics covered:

• Document Object Model (DOM)
• DOM traversal and scraping
• Accessing data that is available on a page
• How to scrape DOM and use that data for GA4 ecommerce
• How to apply this knowledge in Google Tag Manager
• Practical exercises

Document Object Model (DOM) is not just about fetching values of website elements. It’s also about listening to various events and sending their data to analytics tools. Topics explained:

• DOM events
• How to write a custom event listener
• How to work with JavaScript APIs
• How to apply this knowledge in GTM
• Various exercises

Mistakes happen, that’s normal. What’s important is how you handle them and avoid them in the future. Topics explained:

• Tips on how to debug your code
• How browser developer tools can be used here
• How to handle errors in code and reduce the number of them in the console

There are more JavaScript topics you should learn (but I couldn’t decide where to put them). Hence, this module was born. Topics covered:

• Good practices of JS in Google Tag Manager
• using AI to help you with the code
• Browser storage, dealing with dates/time, etc.

Once you get your JavaScript foundations right, it’s time to look at more use cases. This module contains various situations, and I explain how to solve them with JavaScript and GTM, for example:

• How to build a basic A/B test
• How to fix the format of prices
• How to remove part of the page path
• Tracking form field abandonment, and more

If you complete this course and still don’t understand JS well enough, email me for a refund. No questions asked.