Hi@proecom,

Thanks for sharing this with us.

As a first step, since your buttons have multiple classes, I recommend targeting one of the “common denominator classes” in your added to cart snippet that is consistent for all buttons that isn’t changing i.e. btn--add-to-cart

If that doesn’t work, you can try targeting the parent class telling it to find any nested buttons.  This would require a query selector as oppose to getElementByClassname:

<script type="text/javascript">
	var _learnq = _learnq ||  ];
	document.querySelector(".INSERT_CLASS_HERE").addEventListener('click',function (){
 		_learnq.push(l'track', 'Added to Cart', item]);
	});
</script>

Let’s say this is your set-up: 

<div class="parent-div">
 <button class="btn--add-to-cart">Add To Cart</button>
</div>

 You could adapt the querySelector portion to something like:

document.querySelector('div.parent-div > button')

I hope that’s helpful.