fix: browser detection (#8315)

Update browser detection logic: Detect either window or web worker (WorkerGlobalScope).
This updates the implementation to `isBrowser()` and adds a new function `isWebWorker()`.

Fixes #8299 #8284

.changeset/chilly-moons-play.md

@@ -0,0 +1,5 @@
+---
+'@firebase/util': patch
+---
+
+fix: browser detection (detect either window or web worker)

.changeset/fifty-mayflies-hug.md

@@ -0,0 +1,5 @@
+---
+'@firebase/app': patch
+---
+
+fix: server app should initialize in web workers

packages/app/src/api.ts

@@ -48,7 +48,12 @@ import {
   LogOptions,
   setUserLogHandler
 } from '@firebase/logger';
-import { deepEqual, getDefaultAppConfig, isBrowser } from '@firebase/util';
+import {
+  deepEqual,
+  getDefaultAppConfig,
+  isBrowser,
+  isWebWorker
+} from '@firebase/util';
 
 export { FirebaseError } from '@firebase/util';
 
@@ -230,7 +235,7 @@ export function initializeServerApp(
   _options: FirebaseOptions | FirebaseApp,
   _serverAppConfig: FirebaseServerAppSettings
 ): FirebaseServerApp {
-  if (isBrowser()) {
+  if (isBrowser() && !isWebWorker()) {
     // FirebaseServerApp isn't designed to be run in browsers.
     throw ERROR_FACTORY.create(AppError.INVALID_SERVER_APP_ENVIRONMENT);
   }

packages/util/src/environment.ts

@@ -18,6 +18,11 @@
 import { CONSTANTS } from './constants';
 import { getDefaults } from './defaults';
 
+/**
+ * Type placeholder for `WorkerGlobalScope` from `webworker`
+ */
+declare class WorkerGlobalScope {}
+
 /**
  * Returns navigator.userAgent string or '' if it's not defined.
  * @return user agent string
@@ -77,7 +82,18 @@ export function isNode(): boolean {
  * Detect Browser Environment
  */
 export function isBrowser(): boolean {
-  return typeof self === 'object' && self.self === self;
+  return typeof window !== 'undefined' || isWebWorker();
+}
+
+/**
+ * Detect Web Worker context
+ */
+export function isWebWorker(): boolean {
+  return (
+    typeof WorkerGlobalScope !== 'undefined' &&
+    typeof self !== 'undefined' &&
+    self instanceof WorkerGlobalScope
+  );
 }
 
 /**