add additionalTrackers to set multiple trackers

See https://developer.matomo.org/guides/tracking-javascript-guide#multiple-piwik-trackers

README.md

@@ -81,7 +81,7 @@ _NOTE: By default, this plugin only generates output when run in production mode
 | `respectDnt`            | (optional) If false, will load all scripts without respecting user preference to `Do Not Track` on browsers. Defaults to `true`.                                                                                                                                                                                   |
 | `dev`                   | (optional) Activate dev mode by setting to `true`. Will load all scripts despite not running in `production` environment. Ignores your local browser's DNT header too. Outputs some information in console about what it is doing. Useful for local testing but careful: all hits will be send like in production. |
 | `enableJSErrorTracking` | (optional) Enable basic JavaScript error tracking and reporting in Matomo by setting to `true`.                                                                                                                                                                                                                    |
-
+| `additionalTrackers`    | (optional) An array of additional trackers to track on different Matomo servers. Additional trackers are objects with the keys `siteId` and `trackerUrl` containing the full URL to the Matomo PHP script. Defaults to `[]`.                                                                                                                                                                                                                    |
 ```js
 plugins: [
   {
@@ -100,7 +100,13 @@ plugins: [
       cookieDomain: '*.example.org',
       localScript: '/piwik.js',
       dev: false,
-      enableJSErrorTracking: true
+      enableJSErrorTracking: true,
+      additionalTrackers: [
+        {
+          siteId: 'ADDITIONAL_SITE_ID',
+          trackerUrl: 'https://ADDITIONAL_MATOMO_URL.COM/matomo.php'
+        }
+      ]
     }
   }
 ]

src/__tests__/gatsby-ssr.js

@@ -4,7 +4,7 @@
 
 import { onRenderBody } from '../gatsby-ssr'
 
-describe('gatsby-plugin-google-analytics', () => {
+describe('gatsby-plugin-matomo', () => {
   describe('gatsby-ssr', () => {
     describe('onRenderBody', () => {
       describe('in non-production env', () => {
@@ -120,6 +120,20 @@ describe('gatsby-plugin-google-analytics', () => {
           const result = JSON.stringify(setPostBodyComponents.mock.calls[0][0])
           expect(result).not.toMatch(/navigator.doNotTrack/)
         })
+
+        it('sets additionalTrackers', () => {
+          const { setPostBodyComponents } = setup({
+            additionalTrackers: [
+              {
+                siteId: 'TEST_ADDITIONAL_SITE_ID',
+                trackerUrl: 'TEST_ADDITIONAL_TRACKER_URL'
+              }
+            ]
+          })
+          const result = JSON.stringify(setPostBodyComponents.mock.calls[0][0])
+          expect(result).toMatch(/TEST_ADDITIONAL_SITE_ID/)
+          expect(result).toMatch(/TEST_ADDITIONAL_TRACKER_URL/)
+        })
       })
     })
   })

src/gatsby-ssr.js

@@ -14,7 +14,8 @@ function buildTrackingCode(pluginOptions) {
     disableCookies,
     cookieDomain,
     enableJSErrorTracking,
-    respectDnt = true
+    respectDnt = true,
+    additionalTrackers = []
   } = pluginOptions
 
   const script = localScript ? localScript : `${matomoUrl}/${matomoJsScript}`
@@ -47,6 +48,10 @@ function buildTrackingCode(pluginOptions) {
       window._paq.push(['setTrackerUrl', '${matomoUrl}/${matomoPhpScript}']);
       window._paq.push(['setSiteId', '${siteId}']);
       window._paq.push(['enableHeartBeatTimer']);
+      ${additionalTrackers.map(
+        (t) => `window._paq.push(['addTracker', ${t.trackerUrl}, ${t.siteId}])`
+      )}
+
       window.start = new Date();
 
       (function() {