Slides from Analytics Pioneers Summit (July 2025). Note: This is the condensed version without Lego references or LinkedIn bashing ;)

1. JavaScript in GTM: Good or Bad?
how to avoid JS + how to use it
Markus Baersch

2. Avoiding JS
You might not need JS!

3. Avoid JS: Facebook via template - ecom with one tag
● Facebook Tag Template:
github.com/jabjabonlinemarketing/
FacebookPixel-by-JabJab

4. Avoid JS: Use community templates whenever you can (even if they might be slower)

5. Avoiding JS
use standard elements
JS… because: why not?
...should be a standard regex variable

6. Build!
markus-baersch.de/gtmbook

7. Avoid JS: localStorage / sessionStorage

8. JS as a Tool
JS in console? Okay!
Test CSS selectors in console…
push events
and data…
…debug stuff

9. JS as a Tool
JS in console? Okay!
Test code in console with {{variables}}?
https://gist.github.com/mbaersch/

10. JS as a Tool
JS in console? Okay!
Test code in console with {{variables}}?
https://gist.github.com/mbaersch/

11. Using JS
… in JS variables
Return a function…
or several functions in a “Lib” variable!
16 / 32 ;)

12. Using JS
… in JS variables
Using functions from “Lib”

14. Using JS
… in JS variables
Minimize calls / cache results!
Use long & descriptive names and / or use own
namespace in global scope / persistence!

15. Using JS
… in JS variables Access dataLayer directly (if no other
references for a dataLayer variable)
Logging? Only in debug mode

16. Using JS
Useless knowledge(?)
Push to dataLayer without changing the
actual JS object
… but in GTM (after the next event):
A smart way for sharing sensible
data “only” with your GTM?

17. Hide personal data?

18. Using JS
… in HTML tags
IIFE
“Immediately Invoked
Function Expression”

19. Using JS
GTM vs ES6
Most cases: just convert ES6

20. ES6 errors: 90+% are just const, let, and arrow functions

21. Using JS
Even ChatGPT can do it
but TEST, TEST, TEST!

22. ES6 errors: … if it is a tag and you cannot avoid ES6…

23. ES6 errors: … add a “text/gtmscript” attribute
… but remember: skipping validation means: a broken site is 100% on you ;)

24. Done ;)

25. Thank You!
markus-baersch.de/slideshare
markus-baersch.de/podcast
markus-baersch.de/youtube