Add function to remove UA cookies

This function simply gets rid of cookies associated with UA and our old UA properties.

__tests__/cookie-functions.test.mjs

@@ -301,4 +301,16 @@ describe('Cookie settings', () => {
       expect(document.cookie).toEqual('')
     })
   })
+
+  describe('removeUACookies', () => {
+    it('removes cookies specifc to UA', () => {
+      document.cookie = '_gid=test'
+      document.cookie = '_gat_UA-26179049-17=test'
+      document.cookie = '_gat_UA-116229859-1=test'
+
+      CookieHelpers.removeUACookies()
+
+      expect(document.cookie).toEqual('')
+    })
+  })
 })

src/javascripts/application.mjs

@@ -7,7 +7,8 @@ import BackToTop from './components/back-to-top.mjs'
 import CookieBanner from './components/cookie-banner.mjs'
 import {
   getConsentCookie,
-  isValidConsentCookie
+  isValidConsentCookie,
+  removeUACookies
 } from './components/cookie-functions.mjs'
 import CookiesPage from './components/cookies-page.mjs'
 import Copy from './components/copy.mjs'
@@ -34,6 +35,10 @@ if ($cookieBanner) {
 const userConsent = getConsentCookie()
 if (userConsent && isValidConsentCookie(userConsent) && userConsent.analytics) {
   loadAnalytics()
+
+  // Remove UA cookies if the user previously had them set or Google attempts
+  // to set them
+  removeUACookies()
 }
 
 // Initialise example frames

src/javascripts/components/cookie-functions.mjs

@@ -174,6 +174,9 @@ export function resetCookies() {
       window[`ga-disable-G-${TRACKING_PREVIEW_ID}`] = false
       window[`ga-disable-G-${TRACKING_LIVE_ID}`] = false
       loadAnalytics()
+
+      // Unset UA cookies if they've been set by GTM
+      removeUACookies()
     } else {
       // Disable GA if not allowed
       window[`ga-disable-G-${TRACKING_PREVIEW_ID}`] = true
@@ -192,6 +195,24 @@ export function resetCookies() {
   }
 }
 
+/**
+ * Remove UA cookies for user and prevent Google setting them.
+ *
+ * We've migrated our analytics from UA (Univesal Analytics) to GA4, however
+ * users may still have the UA cookie set from our previous implementation.
+ * Additionally, our UA properties are scheduled for deletion but until they are
+ * entirely deleted, GTM is still setting UA cookies.
+ */
+export function removeUACookies() {
+  for (const UACookie of [
+    '_gid',
+    '_gat_UA-26179049-17',
+    '_gat_UA-116229859-1'
+  ]) {
+    Cookie(UACookie, null)
+  }
+}
+
 /**
  * Check if user allows cookie category
  *