Add cross domain tracking to Tracker object

docs/analytics.md

@@ -160,3 +160,15 @@ Pull `print-intent.js` into your project, and initialise it after analytics (see
 ## Error tracking
 
 Pull `error-tracking.js` into your project, and initialise it after analytics (see [Create an analytics tracker, above](#create-an-analytics-tracker)), to track JavaScript errors.
+
+## Tracking across domains
+
+Once a Tracker instance has been created, tracking across domains can be set up
+for pages like:
+
+```js
+GOVUK.analytics.addLinkedTrackerDomain(trackerIdHere, nameForTracker, domainToLinkTo);
+```
+
+Once this is done hits to that page will be tracked in both your local and the
+named tracker, and sessions will persist to the other domain.

javascripts/govuk/analytics/google-analytics-universal-tracker.js

@@ -89,6 +89,29 @@
     });
   };
 
+  /*
+   https://developers.google.com/analytics/devguides/collection/analyticsjs/cross-domain
+   trackerId - the UA account code to track the domain against
+   name      - name for the tracker
+   domain    - the domain to track
+  */
+  GoogleAnalyticsUniversalTracker.prototype.addLinkedTrackerDomain = function(trackerId, name, domain) {
+    sendToGa('create',
+             trackerId,
+             'auto',
+             {'name': name});
+    // Load the plugin.
+    sendToGa('require', 'linker');
+    sendToGa(name + '.require', 'linker');
+
+    // Define which domains to autoLink.
+    sendToGa('linker:autoLink', [domain]);
+    sendToGa(name + '.linker:autoLink', [domain]);
+
+    sendToGa(name + '.set', 'anonymizeIp', true);
+    sendToGa(name + '.send', 'pageview');
+  };
+
   // https://developers.google.com/analytics/devguides/collection/analyticsjs/custom-dims-mets
   GoogleAnalyticsUniversalTracker.prototype.setDimension = function(index, value) {
     sendToGa('set', 'dimension' + index, String(value));

javascripts/govuk/analytics/tracker.js

@@ -46,5 +46,12 @@
     this.classic.setCustomVariable(index, value, name, scope);
   };
 
+  /*
+   Add a beacon to track a page in another GA account on another domain.
+   */
+  Tracker.prototype.addLinkedTrackerDomain = function(trackerId, name, domain) {
+    this.universal.addLinkedTrackerDomain(trackerId, name, domain);
+  };
+
   GOVUK.Tracker = Tracker;
 })();

spec/unit/analytics/TrackerSpec.js

@@ -71,4 +71,25 @@ describe("GOVUK.Tracker", function() {
     });
   });
 
+  describe('when adding a linked domain', function() {
+    beforeEach(function() {
+      tracker = new GOVUK.Tracker(this.config);
+    });
+
+    it('adds a linked domain to universal only', function() {
+      window._gaq = [];
+      tracker.addLinkedTrackerDomain('1234', 'test', 'www.example.com');
+
+      expect(window._gaq).toEqual([]);
+      var allArgs = window.ga.calls.allArgs()
+      expect(allArgs).toContain(['create', '1234', 'auto', {'name': 'test'}]);
+      expect(allArgs).toContain(['require', 'linker']);
+      expect(allArgs).toContain(['test.require', 'linker']);
+      expect(allArgs).toContain(['linker:autoLink', ['www.example.com']]);
+      expect(allArgs).toContain(['test.linker:autoLink', ['www.example.com']]);
+      expect(allArgs).toContain(['test.set', 'anonymizeIp', true]);
+      expect(allArgs).toContain(['test.send', 'pageview']);
+    });
+  });
+
 });