In this post, I’ll walk you through a tutorial on how to create a Google Tag Manager extension. This extension will be a new listener, whose sole job is to listen for changes in the HTML and CSS markup on the page.
The reason I’m teaching you how to create a DOM listener is simple. Ever so often I come across people asking for help, but they are unable to touch on-page code.
![](https://www.simoahava.com/images/2014/04/test-page.jpg)