Fix transaction interference in v9

packages/database/src/core/view/EventRegistration.ts

@@ -71,8 +71,9 @@ export class CallbackContext {
   matches(other: CallbackContext): boolean {
     return (
       this.snapshotCallback === other.snapshotCallback ||
-      (this.snapshotCallback.userCallback ===
-        other.snapshotCallback.userCallback &&
+      (this.snapshotCallback.userCallback !== undefined &&
+        this.snapshotCallback.userCallback ===
+          other.snapshotCallback.userCallback &&
         this.snapshotCallback.context === other.snapshotCallback.context)
     );
   }

packages/database/test/exp/integration.test.ts

@@ -17,15 +17,18 @@
 
 // eslint-disable-next-line import/no-extraneous-dependencies
 import { initializeApp, deleteApp } from '@firebase/app-exp';
+import { Deferred } from '@firebase/util';
 import { expect } from 'chai';
 
 import {
   get,
   getDatabase,
   goOffline,
   goOnline,
+  push,
   ref,
-  refFromURL
+  refFromURL,
+  runTransaction
 } from '../../exp/index';
 import { onValue, set } from '../../src/exp/Reference_impl';
 import { EventAccumulatorFactory } from '../helpers/EventAccumulator';
@@ -150,4 +153,36 @@ describe('Database@exp Tests', () => {
     expect(() => ref(db)).to.throw('Cannot call ref on a deleted database.');
     defaultApp = undefined;
   });
+
+  it('Can listen to transaction changes', async () => {
+    // Repro for https://github.com/firebase/firebase-js-sdk/issues/5195
+    let latestValue = 0;
+
+    let deferred = new Deferred<void>();
+
+    const database = getDatabase(defaultApp);
+    const counterRef = push(ref(database, 'counter'));
+
+    onValue(counterRef, snap => {
+      latestValue = snap.val();
+      deferred.resolve();
+    });
+
+    async function incrementViaTransaction() {
+      deferred = new Deferred<void>();
+      await runTransaction(counterRef, currentData => {
+        return currentData + 1;
+      });
+      // Wait for the snapshot listener to fire. They are not invoked inline
+      // for transactions.
+      await deferred.promise;
+    }
+
+    expect(latestValue).to.equal(0);
+
+    await incrementViaTransaction();
+    expect(latestValue).to.equal(1);
+    await incrementViaTransaction();
+    expect(latestValue).to.equal(2);
+  });
 });

packages/database/test/transaction.test.ts

@@ -1500,4 +1500,34 @@ describe('Transaction Tests', () => {
       done();
     });
   });
+
+  it('Can listen to transaction changes', async () => {
+    // Repro for https://github.com/firebase/firebase-js-sdk/issues/5195
+    let latestValue = 0;
+
+    const ref = getRandomNode() as Reference;
+
+    let deferred = new Deferred<void>();
+    ref.on('value', snap => {
+      latestValue = snap.val() as number;
+      deferred.resolve();
+    });
+
+    async function incrementViaTransaction() {
+      deferred = new Deferred<void>();
+      await ref.transaction(currentData => {
+        return (currentData as number) + 1;
+      });
+      // Wait for the snapshot listener to fire. They are not invoked inline
+      // for transactions.
+      await deferred.promise;
+    }
+
+    expect(latestValue).to.equal(0);
+
+    await incrementViaTransaction();
+    expect(latestValue).to.equal(1);
+    await incrementViaTransaction();
+    expect(latestValue).to.equal(2);
+  });
 });