Use 'pagehide' for page termination by default.

packages/firestore/src/local/indexeddb_persistence.ts

@@ -23,7 +23,7 @@ import { debugAssert } from '../util/assert';
 import { AsyncQueue, DelayedOperation, TimerId } from '../util/async_queue';
 import { Code, FirestoreError } from '../util/error';
 import { logDebug, logError } from '../util/log';
-import { DocumentLike, WindowLike } from '../util/types';
+import { DocumentLike, WindowLike, terminationEvent } from '../util/types';
 
 import { BundleCache } from './bundle_cache';
 import { IndexManager } from './index_manager';
@@ -966,7 +966,10 @@ export class IndexedDbPersistence implements Persistence {
           return this.shutdown();
         });
       };
-      this.window.addEventListener('unload', this.windowUnloadHandler);
+      this.window.addEventListener(
+        terminationEvent(this.window),
+        this.windowUnloadHandler
+      );
     }
   }
 
@@ -976,7 +979,10 @@ export class IndexedDbPersistence implements Persistence {
         typeof this.window?.removeEventListener === 'function',
         "Expected 'window.removeEventListener' to be a function"
       );
-      this.window!.removeEventListener('unload', this.windowUnloadHandler);
+      this.window!.removeEventListener(
+        terminationEvent(this.window),
+        this.windowUnloadHandler
+      );
       this.windowUnloadHandler = null;
     }
   }

packages/firestore/src/local/shared_client_state.ts

@@ -32,7 +32,7 @@ import { logError, logDebug } from '../util/log';
 import { primitiveComparator } from '../util/misc';
 import { SortedMap } from '../util/sorted_map';
 import { SortedSet } from '../util/sorted_set';
-import { isSafeInteger, WindowLike } from '../util/types';
+import { isSafeInteger, terminationEvent, WindowLike } from '../util/types';
 
 import {
   CLIENT_STATE_KEY_PREFIX,
@@ -613,7 +613,9 @@ export class WebStorageSharedClientState implements SharedClientState {
 
     // Register a window unload hook to remove the client metadata entry from
     // WebStorage even if `shutdown()` was not called.
-    this.window.addEventListener('unload', () => this.shutdown());
+    this.window.addEventListener(terminationEvent(this.window), () =>
+      this.shutdown()
+    );
 
     this.started = true;
   }

packages/firestore/src/util/types.ts

@@ -59,6 +59,14 @@ export interface WindowLike {
   removeEventListener(type: string, listener: EventListener): void;
 }
 
+/**
+ * Returns the page termination event to listen to. 'pagehide' is recommended
+ * if available, it falls back to the less reliable 'unload'.
+ */
+export function terminationEvent(window: WindowLike | null): string {
+  return 'onpagehide' in window! ? 'pagehide' : 'unload';
+}
+
 /** The subset of the browser's Document interface used by the SDK. */
 export interface DocumentLike {
   readonly visibilityState: VisibilityState;