Improve the analytics.js shim to handle more ways of using the ga API (…

…#40)

It turns out that a website can do something like

    ga(tracker => { ... });

and the inline function should be called. That wasn't handled yet, so
let's add the necessary logic from Mozilla's shim script[1] (but
adjusted as necessary).

It also turns out that websites sometimes have their own inline
definition of ga(), that assigns any call arguments to the ga.q
queue. The calls in the queue are supposed to be made with the real
ga() function, once that has been loaded. This also wasn't handled
yet in our shim.

I notice that we still do not handle further ways of using the ga API,
in the future it might be worth just switching to Mozilla's script
entirely.

1 - https://searchfox.org/mozilla-central/source/browser/extensions/webcompat/shims/google-analytics-and-tag-manager.js

surrogates/analytics.js

@@ -1,3 +1,9 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Partially based on https://searchfox.org/mozilla-central/source/browser/extensions/webcompat/shims/google-analytics-and-tag-manager.js
+
 (() => {
     'use strict';
     const noop = () => {};
@@ -8,17 +14,7 @@
     };
     const gaPointer = window.GoogleAnalyticsObject = (window.GoogleAnalyticsObject === undefined) ? 'ga' : window.GoogleAnalyticsObject;
     const datalayer = window.dataLayer;
-    // execute callback if exists, see https://developers.google.com/analytics/devguides/collection/analyticsjs/field-reference#hitCallback
-    const ga = function () {
-        const params = Array.from(arguments);
-        params.forEach((param) => {
-            if (param instanceof Object && typeof param.hitCallback === 'function') {
-                try {
-                    param.hitCallback();
-                } catch (error) {}
-            }
-        });
-    };
+
     const Tracker = new Proxy({}, {
         get (target, prop) {
             if (prop === 'get') {
@@ -36,6 +32,33 @@
             return noop;
         }
     });
+
+    let callQueue = null;
+    if (window[gaPointer] && Array.isArray(window[gaPointer].q)) {
+        callQueue = window[gaPointer].q;
+    }
+
+    // Execute callback if exists.
+    // Note: There are other ways of using the API that aren't handled here yet.
+    const ga = function () {
+        const params = Array.from(arguments);
+
+        if (params.length === 1 && typeof params[0] === 'function') {
+            try {
+                params[0](Tracker);
+            } catch (error) {}
+            return undefined;
+        }
+
+        // See https://developers.google.com/analytics/devguides/collection/analyticsjs/field-reference#hitCallback
+        params.forEach((param) => {
+            if (param instanceof Object && typeof param.hitCallback === 'function') {
+                try {
+                    param.hitCallback();
+                } catch (error) {}
+            }
+        });
+    };
     ga.answer = 42;
     ga.loaded = true;
     ga.create = function () { return new Proxy({}, noopHandler); };
@@ -50,12 +73,6 @@
         } catch (error) {}
     }
 
-    /* This Source Code Form is subject to the terms of the Mozilla Public
-     * License, v. 2.0. If a copy of the MPL was not distributed with this
-     * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-    // gaplugin wrapper based on Mozilla's Google analytics shim:
-    // https://searchfox.org/mozilla-central/source/browser/extensions/webcompat/shims/google-analytics-and-tag-manager.js
     if (!(window.gaplugins && window.gaplugins.Linker)) {
         window.gaplugins = window.gaplugins || {};
         window.gaplugins.Linker = class {
@@ -68,4 +85,12 @@
             passthrough () {}
         };
     }
+
+    if (callQueue) {
+        for (const args of callQueue) {
+            try {
+                ga(...args);
+            } catch (e) { }
+        }
+    }
 })();