Understanding AJAX Forms and Why They Are Difficult to Track

AJAX forms submit data asynchronously without refreshing the page, making them invisible to traditional page-based tracking methods. To track these submissions effectively, we need a JavaScript listener that detects the completion of any AJAX request and pushes data into GTM's dataLayer.

Creating the Custom JavaScript Listener (Original Code)

To track AJAX events, we will implement a custom JavaScript snippet that listens for AJAX requests and, upon completion, pushes a custom event into the GTM dataLayer.

Create a new "Custom HTML" tag in GTM:

In your GTM container, click Tags → New → Tag Configuration → Custom HTML.

Paste the following original JavaScript snippet into the HTML box:

<script>
(function() {
 function pushAjaxEvent(url, status, response) {
   window.dataLayer = window.dataLayer || [];
   window.dataLayer.push({
     event: 'customAjaxSuccess',
     ajaxData: {
       requestUrl: url,
       responseStatus: status,
       responseText: response
     }
   });
 }

 function interceptAjax() {
   if (window.XMLHttpRequest) {
     var origOpen = XMLHttpRequest.prototype.open;
     var origSend = XMLHttpRequest.prototype.send;

     XMLHttpRequest.prototype.open = function(method, url) {
       this._url = url;
       return origOpen.apply(this, arguments);
     };

     XMLHttpRequest.prototype.send = function() {
       var xhr = this;
       var origOnReadyStateChange = xhr.onreadystatechange;

       xhr.onreadystatechange = function() {
         if (xhr.readyState === 4 && xhr.status === 200) {
           pushAjaxEvent(xhr._url, xhr.status, xhr.responseText);
         }
         if (origOnReadyStateChange) {
           origOnReadyStateChange.apply(xhr, arguments);
         }
       };

       return origSend.apply(xhr, arguments);
     };
   }
 }

 // Start intercepting immediately
 interceptAjax();
})();
</script>

Create a GTM Trigger Based on the Custom Event

With the listener set up, we now create a GTM trigger to respond to this custom event.

In GTM, go to Triggers → New → Custom Event.
Event Name: exactly match the event name pushed by our JavaScript snippet:
customAjaxSuccess
Trigger fires on: All Custom Events.
Name this trigger clearly:
Trigger - AJAX Form Submit
Click Save.

Setting up GA4 Event Tag in GTM

Next, we configure the GA4 event tag to send these tracked AJAX submissions to Google Analytics.

Create a new tag: Tags → New → Tag Configuration → Google Analytics: GA4 Event.
Configuration Tag: Select your GA4 configuration tag.
Event Name: Choose a clear name, e.g., ajax_form_submission.
Under Event Parameters, you can add the following for more detailed tracking:

Parameter Name	Value (from Data Layer)
ajax_url	{{DLV - ajaxData.requestUrl}}
ajax_status	{{DLV - ajaxData.responseStatus}}
ajax_response	{{DLV - ajaxData.responseText}} (Optional, ensure no sensitive data)

Creating Data Layer Variables:

To access these parameters, first create Data Layer variables in GTM:

Go to Variables → New → Data Layer Variable.

For URL:
Name: DLV - ajaxData.requestUrl
Data Layer Variable Name: ajaxData.requestUrl
For Status:
Name: DLV - ajaxData.responseStatus
Data Layer Variable Name: ajaxData.responseStatus
For Response (optional):
Name: DLV - ajaxData.responseText
Data Layer Variable Name: ajaxData.responseText

Save each variable individually.

Finalizing the Tag:

Triggering: Choose the previously created trigger (Trigger - AJAX Form Submit).
Name the Tag clearly: GA4 - AJAX Form Submission.
Click Save.

Preview, Debug, and Test in GTM

Always test before publishing:

Click Preview in GTM.
Submit an AJAX form on your website.
In GTM Preview, confirm:
The custom event (customAjaxSuccess) triggers.
The GA4 event tag (GA4 - AJAX Form Submission) fires properly.

Verifying Data in Google Analytics (GA4)

After successful debugging:

Go to your GA4 property → Reports → Engagement → Events.
Check for your event (ajax_form_submission).
(Events may take up to 24 hours to appear, or use GA4’s DebugView for real-time verification.)

Advantages of This Custom Listener Approach:

Universal solution: Independent of third-party libraries like jQuery.
Highly scalable: Automatically captures all AJAX requests without needing to alter individual forms.
Rich detail: Provides useful context such as request URLs and statuses.

How to track AJAX form submissions with Google Analytics (GA4) and Google Tag Manager (GTM)

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