diff --git a/packages/performance/src/services/api_service.ts b/packages/performance/src/services/api_service.ts
index 0495bfed165..28bbc5a2954 100644
--- a/packages/performance/src/services/api_service.ts
+++ b/packages/performance/src/services/api_service.ts
@@ -36,19 +36,20 @@ export type EntryType =
   | 'navigation';
 
 /**
- * This class holds a reference to various browser related objects injected by set methods.
+ * This class holds a reference to various browser related objects injected by
+ * set methods.
  */
 export class Api {
-  private performance: Performance;
+  private readonly performance: Performance;
   /** PreformanceObserver constructor function. */
-  private PerformanceObserver: typeof PerformanceObserver;
-  private windowLocation: Location;
-  onFirstInputDelay?: Function;
-  localStorage!: Storage;
-  document: Document;
-  navigator: Navigator;
-
-  constructor(window?: Window) {
+  private readonly PerformanceObserver: typeof PerformanceObserver;
+  private readonly windowLocation: Location;
+  readonly onFirstInputDelay?: Function;
+  readonly localStorage?: Storage;
+  readonly document: Document;
+  readonly navigator: Navigator;
+
+  constructor(readonly window?: Window) {
     if (!window) {
       throw ERROR_FACTORY.create(ErrorCode.NO_WINDOW);
     }
@@ -58,7 +59,8 @@ export class Api {
     this.navigator = window.navigator;
     this.document = window.document;
     if (this.navigator && this.navigator.cookieEnabled) {
-      // If user blocks cookies on the browser, accessing localStorage will throw an exception.
+      // If user blocks cookies on the browser, accessing localStorage will
+      // throw an exception.
       this.localStorage = window.localStorage;
     }
     if (window.perfMetrics && window.perfMetrics.onFirstInputDelay) {
diff --git a/packages/performance/src/services/remote_config_service.ts b/packages/performance/src/services/remote_config_service.ts
index a1e522b3d18..d886f24e35d 100644
--- a/packages/performance/src/services/remote_config_service.ts
+++ b/packages/performance/src/services/remote_config_service.ts
@@ -15,17 +15,18 @@
  * limitations under the License.
  */
 
-import { SettingsService } from './settings_service';
 import {
-  SDK_VERSION,
+  CONFIG_EXPIRY_LOCAL_STORAGE_KEY,
   CONFIG_LOCAL_STORAGE_KEY,
-  CONFIG_EXPIRY_LOCAL_STORAGE_KEY
+  SDK_VERSION
 } from '../constants';
-import { Api } from './api_service';
-import { getAuthTokenPromise } from './iid_service';
 import { consoleLogger } from '../utils/console_logger';
 import { ERROR_FACTORY, ErrorCode } from '../utils/errors';
 
+import { Api } from './api_service';
+import { getAuthTokenPromise } from './iid_service';
+import { SettingsService } from './settings_service';
+
 const REMOTE_CONFIG_SDK_VERSION = '0.0.1';
 
 interface SecondaryConfig {
@@ -71,12 +72,16 @@ export function getConfig(iid: string): Promise<void> {
     .then(config => processConfig(config))
     .then(
       config => storeConfig(config),
-      /** Do nothing for error, use defaults set in settings service. */ () => {}
+      /** Do nothing for error, use defaults set in settings service. */
+      () => {}
     );
 }
 
 function getStoredConfig(): RemoteConfigResponse | undefined {
   const localStorage = Api.getInstance().localStorage;
+  if (!localStorage) {
+    return;
+  }
   const expiryString = localStorage.getItem(CONFIG_EXPIRY_LOCAL_STORAGE_KEY);
   if (!expiryString || !configValid(expiryString)) {
     return;
@@ -95,10 +100,11 @@ function getStoredConfig(): RemoteConfigResponse | undefined {
 }
 
 function storeConfig(config: RemoteConfigResponse | undefined): void {
-  if (!config) {
+  const localStorage = Api.getInstance().localStorage;
+  if (!config || !localStorage) {
     return;
   }
-  const localStorage = Api.getInstance().localStorage;
+
   localStorage.setItem(CONFIG_LOCAL_STORAGE_KEY, JSON.stringify(config));
   localStorage.setItem(
     CONFIG_EXPIRY_LOCAL_STORAGE_KEY,
@@ -122,9 +128,7 @@ function getRemoteConfig(
       const configEndPoint = `https://firebaseremoteconfig.googleapis.com/v1/projects/${projectId}/namespaces/fireperf:fetch?key=${SettingsService.getInstance().getApiKey()}`;
       const request = new Request(configEndPoint, {
         method: 'POST',
-        headers: {
-          Authorization: `${FIS_AUTH_PREFIX} ${authToken}`
-        },
+        headers: { Authorization: `${FIS_AUTH_PREFIX} ${authToken}` },
         /* eslint-disable camelcase */
         body: JSON.stringify({
           app_instance_id: iid,
@@ -163,7 +167,8 @@ function processConfig(
   const settingsServiceInstance = SettingsService.getInstance();
   const entries = config.entries || {};
   if (entries.fpr_enabled !== undefined) {
-    // TODO: Change the assignment of loggingEnabled once the received type is known.
+    // TODO: Change the assignment of loggingEnabled once the received type is
+    // known.
     settingsServiceInstance.loggingEnabled =
       String(entries.fpr_enabled) === 'true';
   } else if (SECONDARY_CONFIGS.loggingEnabled !== undefined) {
diff --git a/packages/performance/src/utils/attributes_utils.ts b/packages/performance/src/utils/attributes_utils.ts
index 0cfa2abe276..0ea8755b1e1 100644
--- a/packages/performance/src/utils/attributes_utils.ts
+++ b/packages/performance/src/utils/attributes_utils.ts
@@ -39,6 +39,19 @@ const enum EffectiveConnectionType {
   CONNECTION_4G = 4
 }
 
+/**
+ * NetworkInformation
+ *
+ * ref: https://developer.mozilla.org/en-US/docs/Web/API/NetworkInformation
+ */
+interface NetworkInformation {
+  readonly effectiveType?: 'slow-2g' | '2g' | '3g' | '4g';
+}
+
+interface NavigatorWithConnection extends Navigator {
+  readonly connection: NetworkInformation;
+}
+
 const RESERVED_ATTRIBUTE_PREFIXES = ['firebase_', 'google_', 'ga_'];
 const ATTRIBUTE_FORMAT_REGEX = new RegExp('^[a-zA-Z]\\w*$');
 const MAX_ATTRIBUTE_NAME_LENGTH = 40;
@@ -72,8 +85,7 @@ export function getVisibilityState(): VisibilityState {
 
 export function getEffectiveConnectionType(): EffectiveConnectionType {
   const navigator = Api.getInstance().navigator;
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  const navigatorConnection = (navigator as any).connection;
+  const navigatorConnection = (navigator as NavigatorWithConnection).connection;
   const effectiveType =
     navigatorConnection && navigatorConnection.effectiveType;
   switch (effectiveType) {