provide empty window.ga(...) when GA_ID is absent

Author: Christopher Willis-Ford

src/lib/analytics.js

@@ -8,6 +8,13 @@ if (GA_ID) {
         sampleRate: (process.env.NODE_ENV === 'production') ? 100 : 0,
         forceSSL: true
     });
+} else {
+    window.ga = () => {
+        // The `react-ga` module calls this function to implement all Google Analytics calls. Providing an empty
+        // function effectively disables `react-ga`. This is similar to the `testModeAPI` feature of `react-ga` except
+        // that `testModeAPI` logs the arguments of every call into an array. That's nice for testing purposes but
+        // would look like a memory leak in a live program.
+    };
 }
 
 export default GoogleAnalytics;