Access event details in tag from "Custom Event" trigger?

Tag Manager
1

My ultimate goal is to execute a custom HTML tag with data from a custom event when that event fires. If I’m going about this the wrong way, please let me know.

What I have now:

  • an event listener that pushes the event into _mtm: _mtm.push({‘event’: ‘EventName’, ‘details’: eventDetails});
  • a Custom Event trigger listening for ‘EventName’
  • a Custom HTML tag that the ‘EventName’ trigger triggers

I can see the Custom HTML tag firing, but I cannot figure out how to access anything from eventDetails in that tag.

Obviously, I can just store the event in a variable, but that’s a hack that doesn’t scale well if my event fires multiple times in quick succession. Is there a way to reference the ‘details’ object I pushed into ‘_mtm’? Or, is there some other, better way of triggering the Custom HTML tag with that data?

2

You can access the variables from the data layer through the Custom HTML tag see Tag Manager JavaScript API: API Reference - Matomo Analytics (formerly Piwik Analytics) - Developer Docs - v3

This would be eg something like MatomoTagManager.dataLayer.get('details')

3

That works for me today: the events I’m tracking are few and far between on the page.

Is there a way I can add a feature request to get at details for “this” invocation of the tag, in case I want to track an event that comes in more frequently? I can see MatomoTagManager.dataLayer.get('details') becoming a race condition if the event fires often enough (eg., say I have images outside the viewport that are loaded when the user scrolls “close enough” to them that they’re needed and initiating a download; getting the ImageDownloadStarted event from the data layer would make it nigh impossible to determine which images were actually pulled in on a gallery page).

4

Well, in theory it should be the recent content even if fired multiple times within short period since JS is a single thread and the custom HTML tag would be always executed immediately and the details would be recent.

5

That is an excellent point which I hadn’t considered, and with which testing seems to agree. Thank you!