Allow for usage of snowplow callback without this

snowplow · Jan 22, 2025 · 9dfdec6 · 9dfdec6
1 parent 5f01e36
commit 9dfdec6
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diff --git a/trackers/javascript-tracker/src/in_queue.ts b/trackers/javascript-tracker/src/in_queue.ts
@@ -265,6 +265,11 @@ export function InQueueManager(functionName: string, asyncQueue: Array<unknown>)
             // Strip GlobalSnowplowNamespace from ID
             fnTrackers[tracker.id.replace(`${functionName}_`, '')] = tracker;
           }
+
+          // Append the `fnTrackers` object to the parameterArray, to allow it to be
+          // accessed as the final argument in the callback, useful in environments that don't support `this` (GTM)
+          Array.prototype.push.call(parameterArray, fnTrackers);
+
           input.apply(fnTrackers, parameterArray);
         } catch (ex) {
           LOG.error('Tracker callback failed', ex);

diff --git a/trackers/javascript-tracker/test/unit/in_queue.test.ts b/trackers/javascript-tracker/test/unit/in_queue.test.ts
@@ -67,6 +67,9 @@ describe('InQueueManager', () => {
       setUserId: function (s?: string | null) {
         userId = s;
       },
+      getUserId: function () {
+        return userId;
+      },
       trackPageView: function () {
         output = attribute;
       },
@@ -183,4 +186,100 @@ describe('InQueueManager', () => {
       ]);
     }).not.toThrow();
   });
+
+  it('Executing a custom callback with arguments should pass the arguments to the callback parameters', () => {
+    asyncQueue.push([
+      function (a: number, b: number) {
+        expect(a).toEqual(1);
+        expect(b).toEqual(2);
+      },
+      1,
+      2,
+    ]);
+  });
+
+  it('A custom callback with arguments provided will pass those arguments into the callback parameters', () => {
+    const tracker = newTracker('sp1');
+    mockTrackers.sp1 = tracker;
+
+    asyncQueue.push([
+      function (a: number, b: number) {
+        expect(a).toEqual(1);
+        expect(b).toEqual(2);
+      },
+      1,
+      2,
+    ]);
+
+    delete mockTrackers.sp1;
+  });
+
+  it('The callback will be passed the tracker dictionary as the final argument', () => {
+    const mockTracker = newTracker('sp1');
+    mockTracker.setUserId('foo');
+    mockTrackers.sp1 = mockTracker;
+
+    asyncQueue.push([
+      function (a: number, b: number, trackers: Record<string, any>) {
+        expect(a).toEqual(1);
+        expect(b).toEqual(2);
+
+        const tracker = trackers.sp1;
+
+        expect(tracker).toEqual(mockTracker);
+        expect(tracker.getUserId()).toEqual('foo');
+      },
+      1,
+      2,
+    ]);
+    delete mockTrackers.sp1;
+  });
+
+  it('The callback will be passed the tracker dictionary as the argument if there is only one parameter', () => {
+    const mockTracker = newTracker('sp1');
+    mockTracker.setUserId('foo');
+    mockTrackers.sp1 = mockTracker;
+
+    asyncQueue.push([
+      function (trackers: Record<string, any>) {
+        const tracker = trackers.sp1;
+
+        expect(tracker).toEqual(mockTracker);
+        expect(tracker.getUserId()).toEqual('foo');
+      },
+    ]);
+    delete mockTrackers.sp1;
+  });
+
+  it('The callback can access the tracker dictionary using both `this` and the first argument', () => {
+    const mockTracker = newTracker('sp1');
+    mockTracker.setUserId('foo');
+    mockTrackers.sp1 = mockTracker;
+
+    asyncQueue.push([
+      function (this: any, trackers: Record<string, any>) {
+        expect(this.sp1).toEqual(mockTrackers.sp1);
+        expect(trackers.sp1).toEqual(mockTrackers.sp1);
+      },
+    ]);
+    delete mockTrackers.sp1;
+  });
+
+  it('The callback can access the tracker dictionary using both `this` and  the last argument, along with arguments', () => {
+    const mockTracker = newTracker('sp1');
+    mockTracker.setUserId('foo');
+    mockTrackers.sp1 = mockTracker;
+
+    asyncQueue.push([
+      function (this: any, a: number, b: number, trackers: Record<string, any>) {
+        expect(this.sp1).toEqual(mockTrackers.sp1);
+        expect(a).toEqual(1);
+        expect(b).toEqual(2);
+        expect(trackers.sp1).toEqual(mockTrackers.sp1);
+      },
+      1,
+      2,
+    ]);
+    delete mockTrackers.sp1;
+  });
 });