FEATURE: plugins can send more data to Google Tag Manager

app/assets/javascripts/discourse/initializers/page-tracking.js.es6

@@ -1,5 +1,5 @@
 import { cleanDOM } from 'discourse/lib/clean-dom';
-import { startPageTracking } from 'discourse/lib/page-tracker';
+import { startPageTracking, googleTagManagerPageChanged } from 'discourse/lib/page-tracker';
 import { viewTrackingRequired } from 'discourse/lib/ajax';
 
 export default {
@@ -35,15 +35,7 @@ export default {
 
     // And Google Tag Manager too
     if (typeof window.dataLayer !== 'undefined') {
-      appEvents.on('page:changed', data => {
-        window.dataLayer.push({
-          'event': 'virtualPageView',
-          'page': {
-            'title': data.title,
-            'url': data.url
-          }
-        });
-      });
+      appEvents.on('page:changed', googleTagManagerPageChanged);
     }
   }
 };

app/assets/javascripts/discourse/lib/page-tracker.js.es6

@@ -38,3 +38,23 @@ export function startPageTracking(router, appEvents) {
   });
   _started = true;
 }
+
+const _gtmPageChangedCallbacks = [];
+
+export function addGTMPageChangedCallback(callback) {
+  _gtmPageChangedCallbacks.push(callback);
+}
+
+export function googleTagManagerPageChanged(data) {
+  let gtmData = {
+    'event': 'virtualPageView',
+    'page': {
+      'title': data.title,
+      'url': data.url
+    }
+  };
+
+  _.each(_gtmPageChangedCallbacks, callback => callback(gtmData));
+
+  window.dataLayer.push(gtmData);
+}

app/assets/javascripts/discourse/lib/plugin-api.js.es6

@@ -22,9 +22,10 @@ import { registerIconRenderer, replaceIcon } from 'discourse-common/lib/icon-lib
 import { addNavItem } from 'discourse/models/nav-item';
 import { replaceFormatter } from 'discourse/lib/utilities';
 import { modifySelectKit } from "select-kit/mixins/plugin-api";
+import { addGTMPageChangedCallback } from 'discourse/lib/page-tracker';
 
 // If you add any methods to the API ensure you bump up this number
-const PLUGIN_API_VERSION = '0.8.15';
+const PLUGIN_API_VERSION = '0.8.16';
 
 class PluginApi {
   constructor(version, container) {
@@ -619,6 +620,20 @@ class PluginApi {
   modifySelectKit(pluginApiKey) {
     return modifySelectKit(pluginApiKey);
   }
+
+  /**
+  *
+  * Registers a function that can inspect and modify the data that
+  * will be sent to Google Tag Manager when a page changed event is triggered.
+  *
+  * Example:
+  *
+  * addGTMPageChangedCallback( gtmData => gtmData.locale = I18n.currentLocale() )
+  *
+  */
+  addGTMPageChangedCallback(fn) {
+    addGTMPageChangedCallback(fn);
+  }
 }
 
 let _pluginv01;