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pwwolf opened this issue Aug 25, 2022 · 4 comments
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Unable to use custom dataLayerName when multiple copies of gtag.js exist #6565

pwwolf opened this issue Aug 25, 2022 · 4 comments
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api: analytics

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@pwwolf
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pwwolf commented Aug 25, 2022 •
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[REQUIRED] Describe your environment

Operating System version: MacOS 12.4
Browser version: Brave v1.42.97
Firebase SDK version: 9.9.2
Firebase Product: Analytics

[REQUIRED] Describe the problem

I'm using Firebase Analytics on a web site that loads multiple copies of gtag.js with different tracking/measurement IDs, i.e. if I look at the DOM for the site I see several script tags like
<script async src="https://www.googletagmanager.com/gtag/js?id=XXXXXXX"/>

The problem is that if I want to use a custom data layer name, the gtag script tag also needs to have the custom data layer name passed in via a query parameter, &l=custom_datalayer_name. Firebase, won't add a new script tag if one already exists, even if the l query param is different.

It's evident looking at initialize-analytics.ts that the call to findGtagScriptOnPage doesn't take the dataLayerName into account.

  // Detect if user has already put the gtag <script> tag on this page.
  if (!findGtagScriptOnPage()) {
    insertScriptTag(dataLayerName, dynamicConfig.measurementId);
  }

Steps to reproduce:

  1. Have an HTML file that has a gtag script
  2. Load a module that initializes firebase analytics and uses settings to customize the data layer name
  3. Observe that there's no new gtag <script> with the specified datalayer
  4. Log an event
  5. Observe in GA debugger that nothing is sent

Now remove the gtag <script>

  1. Observe that firebase correctly creates a script tag with the l query param
  2. Log an event
  3. Observe the event is sent

Alternatively, remove the settings call with custom dataLayerName and events work too regardless of whether the script tag is present.

Relevant Code:

<html>
  <head>
    <script src="https://www.googletagmanager.com/gtag/js?l=datalayer&id=G-XXXXX" async=""></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());

      gtag('config', 'XXXXX');
    </script>
  </head>
  <body>
    ...
  </body>
</html>
  const app = initializeApp(firebaseConfig);
  settings({ gtagName: "custom_gtag", dataLayerName: "custom_datalayer" });
  const analytics = getAnalytics(app);
  logEvent(analytics, "test_event");
@google-oss-bot
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I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

@hsubox76
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hsubox76 commented Sep 8, 2022

I have one question to ask, we've had complaints in the past from users when gtag was accidentally loaded twice due to a bug, that they got an error in the console (I think only when using the Google Analytics Debugger). Does a second loading of gtag, with a new datalayer name, cause any problems when you do it manually?

@pwwolf
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pwwolf commented Sep 9, 2022

I have seen first-hand a number of sites with a half-dozen copies of gtag loaded without error. Usually they just differ in id. Less commonly do I see the dataLayer modified, but in my own testing it hasn't caused any noticeable error, even with the GA debugger.

@dwyfrequency dwyfrequency mentioned this issue Oct 6, 2022
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@dwyfrequency
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The feature has been released in v9.12.0.

@firebase firebase locked and limited conversation to collaborators Nov 18, 2022
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@pwwolf @dwyfrequency @hsubox76 @google-oss-bot @argzdev