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 using that as an alternative fix to persistence issues should not be considered future-proof. this solution should not be considered future-proof. Updated 12 March 2019 with some minor clarifications.. On 21st February 2019, WebKit announced the release of the latest iteration of Safari’s Intelligent Tracking Prevention (ITP), known as ITP 2.

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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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The jQuery JavaScript library is by almost any means of counting the most popular JavaScript library used in websites around the world. It’s so influential, in fact, that its evolution is tightly bound to the JavaScript standardization effort itself, and it’s an integral part of the JS Foundation’s efforts to build a community for JavaScript developers. Google Tag Manager, similarly, is the most popular tag management system used in websites, globally.

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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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Last updated 9 October 2020: customTask updated to a more stable version. I’m a big fan of Enhanced Ecommerce in Google Analytics. In fact, I think it’s the only valid way to deploy Ecommerce tracking today, especially when using Google Tag Manager. The ability to use a Custom JavaScript variable and the possibility to tackle the full ecommerce funnel are some of the benefits of using Enhanced Ecommerce.

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Last updated 9 October 2020: customTask updated to a more stable version. 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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