Add event tracking to window.GOVUK.analytics

app/assets/javascripts/errorTracking.js sent
events to `window.ga`.

This extends the API of `window.GOVUK.Analytics`
to include support for sending events so all
calls to `window.ga` can use it instead of direct
access.

This use of `window.ga` was missed from the
initial work on `window.GOVUK.Anaytics`.

app/assets/javascripts/analytics/analytics.js

@@ -4,7 +4,7 @@
   window.GOVUK = window.GOVUK || {};
 
   // Stripped-down wrapper for Google Analytics, based on:
-  // https://github.com/alphagov/static/blob/master/app/assets/javascripts/analytics_toolkit/analytics.js
+  // https://github.com/alphagov/static/blob/master/doc/analytics.md
   const Analytics = function (config) {
     window.ga('create', config.trackingId, config.cookieDomain);
 
@@ -34,6 +34,29 @@
 
   };
 
+  // https://developers.google.com/analytics/devguides/collection/analyticsjs/events
+  Analytics.prototype.trackEvent = function (category, action, options) {
+
+    options = options || {};
+
+    var evt = {
+      eventCategory: category,
+      eventAction: action
+    };
+
+    if (options.label) {
+      evt.eventLabel = options.label;
+      delete options.label;
+    }
+
+    if (typeof options === 'object') {
+      $.extend(evt, options);
+    }
+
+    window.ga('send', 'event', evt);
+
+  };
+
   window.GOVUK.Analytics = Analytics;
 
 })(window);

app/assets/javascripts/errorTracking.js

@@ -1,22 +1,22 @@
-(function(Modules) {
+(function(window) {
   "use strict";
 
-  Modules.TrackError = function() {
+  window.GOVUK.Modules.TrackError = function() {
 
     this.start = function(component) {
 
-      if (!ga) return;
+      if (!('analytics' in window.GOVUK)) return;
 
-      ga(
-        'send',
-        'event',
+      window.GOVUK.analytics.trackEvent(
         'Error',
         $(component).data('error-type'),
-        $(component).data('error-label')
+        {
+          'label': $(component).data('error-label')
+        }
       );
 
     };
 
   };
 
-})(window.GOVUK.Modules);
+})(window);

tests/javascripts/analytics/analytics.test.js

@@ -37,7 +37,7 @@ describe("Analytics", () => {
 
   afterEach(() => {
 
-    window.ga.mockReset();
+    window.ga.mockClear();
 
   });
 
@@ -58,10 +58,15 @@ describe("Analytics", () => {
 
   describe("When tracking pageviews", () => {
 
-    test("It sends the right URL for the page if no arguments", () => {
+    beforeEach(() => {
 
+      // clear calls to window.ga from set up
       window.ga.mockClear();
 
+    });
+
+    test("It sends the right URL for the page if no arguments", () => {
+
       jest.spyOn(window, 'location', 'get').mockImplementation(() => {
         return {
           'pathname': '/privacy',
@@ -77,8 +82,6 @@ describe("Analytics", () => {
 
     test("It strips the UUIDs from URLs", () => {
 
-      window.ga.mockClear();
-
       jest.spyOn(window, 'location', 'get').mockImplementation(() => {
         return {
           'pathname': '/services/6658542f-0cad-491f-bec8-ab8457700ead',
@@ -94,4 +97,29 @@ describe("Analytics", () => {
 
   });
 
+  describe("When tracking events", () => {
+
+    beforeEach(() => {
+
+      // clear calls to window.ga from set up
+      window.ga.mockClear();
+
+    });
+
+    test("It sends the right arguments to `ga`", () => {
+
+      analytics.trackEvent('Error', 'Enter a valid email address', {
+        'label': 'email_address'
+      });
+
+      expect(window.ga.mock.calls[0]).toEqual(['send', 'event', {
+        'eventCategory': 'Error',
+        'eventAction': 'Enter a valid email address',
+        'eventLabel': 'email_address'
+      }]);
+
+    });
+
+  });
+
 });

tests/javascripts/errorTracking.test.js

@@ -18,18 +18,23 @@ describe('Error tracking', () => {
   afterEach(() => {
 
     document.body.innerHTML = '';
+    delete window.GOVUK.analytics;
 
   });
 
-  test("It should send the right data to Google Analytics", () => {
+  test("If there is an analytics tracker set up, it should send details of the error to window.GOVUK.analytic", () => {
 
-    window.ga = jest.fn(() => {});
+    window.GOVUK.analytics = {
+      'trackEvent': jest.fn()
+    };
 
     // start the module
     window.GOVUK.modules.start();
 
-    expect(window.ga).toHaveBeenCalled();
-    expect(window.ga.mock.calls[0]).toEqual(['send', 'event', 'Error', 'validation', 'missing field']);
+    expect(window.GOVUK.analytics.trackEvent).toHaveBeenCalled();
+    expect(window.GOVUK.analytics.trackEvent.mock.calls[0]).toEqual(['Error', 'validation', {
+      'label': 'missing field'
+    }]);
 
   });