Resolving Next.js interference with the Google tag's cross-domain measurement linker

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1

The client's problem

Debug & Fix Cross-Domain Tracking Redirect Issue

The Problem

We are experiencing a tracking data loss issue on our advertorial page.
When users click a call-to-action button to navigate to our main website, the URL is not being "decorated" with the necessary GA4 _gl parameters.
This is breaking our cross-domain tracking and attribution.

The Task

We need an expert developer to debug and fix the specific redirect mechanism on our advertorial page.

You will:

Identify the cause: Determine why the gtag.js linker is failing to attach the ?_gl parameter during the redirect process.
Implement a fix: Modify the existing button/link logic (currently in a Next.js/Vercel environment) so that the parameter is reliably appended to the destination URL before navigation occurs.
Verify: Confirm that the full URL string (including the _gl parameter) successfully lands on the main website and is recognized by GA4.

Please briefly explain

  • How you would ensure a GA4 linker parameter is captured and successfully passed during a redirect.
  • How you would solve the "race condition".
2

My analysis

1

There is no «race condition» in your case because a race condition means that «multiple code paths» «are executing at the same time»: en.wikipedia.org/wiki/Race_condition#In_software

2

In your case, the Google tag's cross-domain measurement linker and Next.js operate in a single thread (synchronously), and your problem arises because Next.js prematurely interrupts the click event bubbling, thereby preventing the Google tag's linker from processing the event.

3

The Google tag's linker listens for webpage events at the topmost level (Document) of the DOM.

4

Next.js listens for webpage events at a lower level, on the app's root DOM node (e.g., <div id='__next'>).

5

When a user clicks a link, the click event is processed by Next.js first (due to §4) before reaching the Google tag's linker.
Your Next.js app behaves incorrectly during cross-domain navigation because your developer improperly handled the click event at this step.

6

Upon initiating cross-domain navigation, the browser unloads the webpage, thereby interrupting the event bubbling (§2).

7

Thus, the Google tag's linker simply does not receive control.
The linker adds _gl to the link strictly upon the click event rather than in advance; thus in the scenario of §§3-6 it will not add _gl to the link, which is the root cause of your problem.

8

To solve your problem, it is necessary to change the click event handling at step §5:

8.1

Call preventDefault() on the click event.

8.2

Allow the click event to bubble up the DOM to the document.

8.3

Allow the Google tag's linker to process the event (to append the _gl parameter to the link's href attribute).

8.4

Then, using a previously saved reference to the underlying JavaScript object of the link HTML element, asynchronously read the updated href property of the object and redirect the browser to this URL.