Use 'pagehide' for page termination by default.

Author: wu-hui

packages/firestore/src/local/indexeddb_persistence.ts

@@ -942,6 +942,14 @@ export class IndexedDbPersistence implements Persistence {
     }
   }
 
+  /**
+   * Returns the page termination event to listen to. 'pagehide' is recommended
+   * if available, it falls back to the less reliable 'unload'.
+   */
+  private terminationEvent(): string {
+    return 'onpagehide' in this.window! ? 'pagehide' : 'unload';
+  }
+
   /**
    * Attaches a window.unload handler that will synchronously write our
    * clientId to a "zombie client id" location in LocalStorage. This can be used
@@ -966,7 +974,10 @@ export class IndexedDbPersistence implements Persistence {
           return this.shutdown();
         });
       };
-      this.window.addEventListener('unload', this.windowUnloadHandler);
+      this.window.addEventListener(
+        this.terminationEvent(),
+        this.windowUnloadHandler
+      );
     }
   }
 
@@ -976,7 +987,10 @@ 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(
+        this.terminationEvent(),
+        this.windowUnloadHandler
+      );
       this.windowUnloadHandler = null;
     }
   }