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In Google Tag Manager, the Custom JavaScript variable is an anonymous function with a return statement. It does not take any parameters, and by default it’s impossible to pass any parameters to it, because the Custom JS variable is simply resolved to whatever value the function returns. If it returns a number, for example, passing a parameter to it would make no sense and would result in a TypeError since the variable resolves to a number, not a function.

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Updated 1 October 2019 With ITP 2.3 it looks like Safari is reducing the usefulness of localStorage as well, so this solution should not be considered future-proof. The only stable way to persist client-side data at the moment seems to be HTTP cookies. Updated 7 March 2019 - Added some extra caveats to this solution. Also, be sure to read my article on ITP 2.1, which has far more detail on what Intelligent Tracking Prevention is and how to work with it.

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A recurring question in the Google Tag Manager communities (e.g. product forums) is how to use an Enhanced Ecommerce dataLayer object with the Facebook pixel code? It’s a common question since running a Facebook conversion pixel on a site that also collects data from the store into Google Analytics’ Enhanced Ecommerce reports is probably a very typical scenario. Side note: Since Google+ is about to go the way of the dodo, I’ve created an archive of the entire community which you can browse and make text searches against.

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The Custom HTML tag in Google Tag Manager is splendid. It’s your go-to tool when you need to run arbitrary JavaScript on the webpage. Some might even use it to actually add HTML elements to the page, but I’m willing to bet running JavaScript is its most common use. However, there’s a downside to Custom HTML tags, which is only made more apparent on single-page apps which do not clear the full page when transitioning from one state to another.

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Thanks to the intrepid detective work of Jørn Reidel and Ahmed Marof, it looks like one of the big hurdles for doing a full migration from using the legacy Google Analytics and Google Tag Manager SDKs to the latest Tag Manager + Firebase SDK is now a non-issue. The issue is, of course, Product-scoped Custom Dimensions or more specifically the lack of support thereof. Until now, I’d been holding against recommending the migration to anyone with Enhanced Ecommerce tracking set up simply because the documentation didn’t mention the possibility of sending these custom definitions to Google Analytics.

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If you are enjoying the Element Visibility trigger as much as I am, you’ll be glad to know of a very simple tip that might make your life easier when using Google Tag Manager. The tip is this: If you’ve activated the built-in Click variables, they will be automatically populated with details about the element that caused the Element Visibility trigger to activate! Tip 92: Use Built-in variables to analyze the visible element Yes, it’s confusing they’re still named Click variables, especially since they’re duplicated in the Form variables, and even more so since they can be used with the Element Visibility trigger to identify which element became visibility.

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One of the difficulties of working with Google Tag Manager and the dataLayer structure is that GTM doesn’t preserve history of the items collected into its data model. Or, at least, it doesn’t preserve it in a manner that would let us access it. This is typically a very niche problem, but it does surface every now and then. For example, say you wanted to query whether an event with some specific value has already been pushed into dataLayer.

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Simo Ahava

Husband | Father | Analytics developer
simo (at) simoahava.com

Senior Data Advocate at Reaktor

Finland