Fix: (third-parties) sendGTMEvent not queueing events before GTM init (…

…#68683)

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### What?

sendGTMEvent pushes items to window.datalayer. THe GoogleTagManger (GTM)
client uses this to know what events to the GTM server.

currently if GTM is not ready, instead of adding events to the
dataLayer, it writes a warning to the console saying GTM is not ready.

The PR fixes that by defining the dataLayer if it is undefined so it can
start to queue up events before GTM is ready

### Why?

If GTM init is slow we don't want to loose any events that we want to
send before GTM init has happened we want to queue them up in the
dataLayer



### How?

The PR fixes that by defining the dataLayer if it is undefined so it can
start to queue up events before GTM is ready

Closes NEXT-
Fixes #

fixes #66865 (discussion)
fixes #68678 (issue)

-->

### What?

sendGTMEvent pushes items to window.datalayer. THe GoogleTagManger (GTM)
client uses this to know what events to the GTM server.

currently if GTM is not ready, instead of adding events to the
dataLayer, it writes a warning to the console saying GTM is not ready.

The PR fixes that by defining the dataLayer if it is undefined so it can
start to queue up events before GTM is ready


https://developers.google.com/tag-platform/tag-manager/datalayer#how_data_layer_information_is_processed

### Why?

If GTM init is slow we don't want to loose any events that we want to
send before GTM init has happened we want to queue them up in the
dataLayer

Another use case for this behaviour, is that you can optionally
initialise GoogleTagManager based on environment so you don't pollute
GTM data when developing or running playright tests, but you can still
evaluate what exists on the dataLayer to test if the correct events
would be sent to GTM after testing interactions with the app.

### How?

The PR fixes that by defining the dataLayer if it is undefined so it can
start to queue up events before GTM is ready

Fixes #

fixes #66865 (discussion)
fixes #68678 (issue)

---------

Co-authored-by: JJ Kasper <jj@jjsweb.site>

packages/third-parties/src/google/gtm.tsx

@@ -5,7 +5,7 @@ import Script from 'next/script'
 
 import type { GTMParams } from '../types/google'
 
-let currDataLayerName: string | undefined = undefined
+let currDataLayerName = 'dataLayer'
 
 export function GoogleTagManager(props: GTMParams) {
   const {
@@ -17,9 +17,7 @@ export function GoogleTagManager(props: GTMParams) {
     nonce,
   } = props
 
-  if (currDataLayerName === undefined) {
-    currDataLayerName = dataLayerName
-  }
+  currDataLayerName = dataLayerName
 
   const gtmLayer = dataLayerName !== 'dataLayer' ? `&l=${dataLayerName}` : ''
   const gtmAuth = auth ? `&gtm_auth=${auth}` : ''
@@ -62,17 +60,10 @@ export function GoogleTagManager(props: GTMParams) {
   )
 }
 
-export const sendGTMEvent = (data: Object) => {
-  if (currDataLayerName === undefined) {
-    console.warn(`@next/third-parties: GTM has not been initialized`)
-    return
-  }
-
-  if (window[currDataLayerName]) {
-    window[currDataLayerName].push(data)
-  } else {
-    console.warn(
-      `@next/third-parties: GTM dataLayer ${currDataLayerName} does not exist`
-    )
-  }
+export const sendGTMEvent = (data: Object, dataLayerName?: string) => {
+  // special case if we are sending events before GTM init and we have custom dataLayerName
+  const dataLayer = dataLayerName || currDataLayerName
+  // define dataLayer so we can still queue up events before GTM init
+  window[dataLayer] = window[dataLayer] || []
+  window[dataLayer].push(data)
 }