Pageview Trigger not working in GTM? Here’s How You Can Fix It

Hi Julius,

Thanks for the article - the issue is very real, indeed. However, I have some nits to pick :)

I don't really follow your logic of "must not be defined as a JavaScript variable". Both

dataLayer = []

and

var dataLayer = []

are identical statements in a non-function scope. Both initialize JavaScript variables (there are no non-JavaScript variables in JavaScript..), and both are the same as executing

window.dataLayer = [];

The difference between "var" and no "var" is apparent in function scope. In function scope, "var dataLayer" would scope the variable locally to the function, where as "dataLayer" would climb up the scope chain, trying to find a previously declared instance of the dataLayer variable. If none is found, it plants its roots in the global window scope. Since dataLayer already exists in the global window scope, "var" vs. "no var" is not really relevant.

Also, you should use neither, ever.

First, you never have to use an empty dataLayer initialization if you use GTM, since the container snippet does that for you. Including the empty initialization is redundant and can lead to problems like the one described in this article.

Second, when working with a global structure that might be governed by multiple parties (developers, GTM users, other TMS users), it's very risky to initialize dataLayer with dataLayer = []; even if it's before the container snippet. It's possible that the web server has already created a base dataLayer (e.g. ecommerce data), and having that initialization statement removes any trace of this first object push from dataLayer.

So, I recommend to always use the following syntax when working with dataLayer, regardless of where in the site you do it (before the container snippet, after the container snippet, another JS file):

window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
key: 'value'
});

The first line creates dataLayer IF it hasn't already been created. If it already existed, it simply creates a reference to itself. After that, all key-value pairs are added with .push().

So I agree with your observations in this article, but I don't really agree with the suggested course of action :)

Simo

Yeah, in a perfect world Google's documentation would be correct, and in a perfect world they would listen to the suggestions of the user base recommending them to fix the documentation :) This isn't the only thing that's at fault in the current docs (check the tag setup recommendations in GTM's Enhanced Ecommerce documentation if you really want your jaw to drop).

That's why as a content creator and someone who does a lot of support and outreach I feel obligated to do my best to increase awareness about this. Typically when people use var dataLayer = []; and find their GTM setup breaking completely, they reach out in the Product forums for assistance, or perhaps they'll google for help and find articles such as this one.

So I completely agree - Google's documentation should be up-to-date and not full of dangerous pitfalls like this!

Thanks again for the article!

Simo

Hi.
I have set up Google Tag Manager for view, out bound link, and timer.. and it work supposed to be. However, when I added other trigger like form submission and Youtube Video , no trigger have been detected on preview mode.

FYI, the blog is new and no change coding have been modify since I start using Tag manager.

Do you know why only my first 3 triggers is working and why the other is not seem to work on my blog.

This article really helped me out of a bind. The purchase tag was firing but didn't come over with the purchase value. I had to play with the trigger settings to have it fire when the DOM Object was ready because the template variable didn't load yet.

Thanks for the help!

I am having trouble pushing custom variables to dataLayer, since they are available and hence set much lower on the page after the HEAD tag ( where the Tag Manager code is) is generated. The pageview tag is unable to read the dataLayer variables set, since it is fired before the dataLayer push happens.
I would like to know what is the best way to handle this issue.

We have implemented Tag Manager on our PDF Converter sales web page and always no data was send on that page. And we have been following TM documentation where it is said that dataLayer = [{}] must be added before TM container. We have replaced with push and now everything works fine! Thank you for your blog post!

Thanks. That helped a lot.
I had var dataLayer = []; in my .js file. It was working fine.
Suddenly all events stopped firing except dataLayer.push events which I was sending through JavaScript. Page view event wasn't firing as well. I don't know why it wasn't working as the code was mostly same. Adding <script>var dataLayer = [];</script> before gtm script in head helped :)

Just want to let you know this saved me from a huge headache trying to figure out what was going on. My variables were all capturing except under "Pageview" scenarios and I was looking at the option of switching to "DOM Ready" which would cause me to compromise by losing some Analytics stats (particularly bounce detection).

I have a feeling most people who use GTM don't implement much other than sticking it on a page along with desired tags. The annoyance of not having this stuff clearly documented by Google creates is hard to put into words.

It's times like these I sometimes consider creating my own version of something. Ultimately all GTM is doing is orchestrating tag injection and custom JS into pages with a management interface for non-techs. It's not rocket science but their implementation makes it feel like it they purposefully made it that way.

Hey, thanks for the post! I have the same issue, but i dont know how to fix it, because i use the gtm4wp plugin, i am not a developer. My events are fine. But the pageview trigger does not appear in the preview and debug mode. All my pageview tags are firing in the container load trigger, this is good? Should i worry about it?

Thanks Julius!