feat: add offline mode

packages/analytics-browser/src/browser-client.ts

@@ -31,6 +31,7 @@ import { formInteractionTracking } from './plugins/form-interaction-tracking';
 import { fileDownloadTracking } from './plugins/file-download-tracking';
 import { DEFAULT_SESSION_END_EVENT, DEFAULT_SESSION_START_EVENT } from './constants';
 import { detNotify } from './det-notification';
+import { networkConnectivityCheckerPlugin } from './plugins/network-connectivity-checker';
 
 export class AmplitudeBrowser extends AmplitudeCore implements BrowserClient {
   // eslint-disable-next-line @typescript-eslint/ban-ts-comment
@@ -86,6 +87,9 @@ export class AmplitudeBrowser extends AmplitudeCore implements BrowserClient {
 
     // Step 4: Install plugins
     // Do not track any events before this
+    if (this.config.offline !== null) {
+      await this.add(networkConnectivityCheckerPlugin()).promise;
+    }
     await this.add(new Destination()).promise;
     await this.add(new Context()).promise;
     await this.add(new IdentityEventSender()).promise;

packages/analytics-browser/src/config.ts

@@ -60,6 +60,7 @@ export class BrowserConfig extends Config implements IBrowserConfig {
     public loggerProvider: ILogger = new Logger(),
     public logLevel: LogLevel = LogLevel.Warn,
     public minIdLength?: number,
+    public offline: boolean | null = false,
     optOut = false,
     public partnerId?: string,
     public plan?: Plan,
@@ -236,6 +237,7 @@ export const useBrowserConfig = async (
     options.loggerProvider,
     options.logLevel,
     options.minIdLength,
+    options.offline,
     optOut,
     options.partnerId,
     options.plan,

packages/analytics-browser/src/plugins/network-connectivity-checker.ts

@@ -0,0 +1,61 @@
+import { getGlobalScope } from '@amplitude/analytics-client-common';
+import { BeforePlugin, BrowserClient } from '@amplitude/analytics-types';
+import { BrowserConfig } from 'src/config';
+
+interface EventListener {
+  type: 'online' | 'offline';
+  handler: () => void;
+}
+
+export const networkConnectivityCheckerPlugin = (): BeforePlugin => {
+  const name = '@amplitude/plugin-network-checker-browser';
+  const type = 'before' as const;
+  const globalScope = getGlobalScope();
+  let eventListeners: EventListener[] = [];
+
+  const addNetworkListener = (type: 'online' | 'offline', handler: () => void) => {
+    if (globalScope) {
+      globalScope.addEventListener(type, handler);
+      eventListeners.push({
+        type,
+        handler,
+      });
+    }
+  };
+
+  const removeNetworkListeners = () => {
+    eventListeners.forEach(({ type, handler }) => {
+      if (globalScope) {
+        globalScope.removeEventListener(type, handler);
+      }
+    });
+    eventListeners = [];
+  };
+
+  const setup = async (config: BrowserConfig, amplitude: BrowserClient) => {
+    config.offline = !navigator.onLine;
+
+    addNetworkListener('online', () => {
+      config.offline = false;
+      // Flush immediately will cause ERR_NETWORK_CHANGED
+      setTimeout(() => {
+        amplitude.flush();
+      }, config.flushIntervalMillis);
+    });
+
+    addNetworkListener('offline', () => {
+      config.offline = true;
+    });
+  };
+
+  const teardown = async () => {
+    removeNetworkListeners();
+  };
+
+  return {
+    name,
+    type,
+    setup,
+    teardown,
+  };
+};

packages/analytics-browser/test/browser-client.test.ts

@@ -10,9 +10,11 @@ import {
   getCookieName,
 } from '@amplitude/analytics-client-common';
 import * as SnippetHelper from '../src/utils/snippet-helper';
+import * as AnalyticsClientCommon from '@amplitude/analytics-client-common';
 import * as fileDownloadTracking from '../src/plugins/file-download-tracking';
 import * as formInteractionTracking from '../src/plugins/form-interaction-tracking';
 import * as webAttributionPlugin from '@amplitude/plugin-web-attribution-browser';
+import * as networkConnectivityChecker from '../src/plugins/network-connectivity-checker';
 
 describe('browser-client', () => {
   let apiKey = '';
@@ -261,6 +263,83 @@ describe('browser-client', () => {
       }).promise;
       expect(webAttributionPluginPlugin).toHaveBeenCalledTimes(1);
     });
+
+    test('should add network connectivity checker plugin by default', async () => {
+      const networkConnectivityCheckerPlugin = jest.spyOn(
+        networkConnectivityChecker,
+        'networkConnectivityCheckerPlugin',
+      );
+      await client.init(apiKey, userId).promise;
+      expect(networkConnectivityCheckerPlugin).toHaveBeenCalledTimes(1);
+    });
+
+    test('should not add network connectivity checker plugin if offline is null', async () => {
+      const networkConnectivityCheckerPlugin = jest.spyOn(
+        networkConnectivityChecker,
+        'networkConnectivityCheckerPlugin',
+      );
+      await client.init(apiKey, userId, {
+        offline: null,
+      }).promise;
+      expect(networkConnectivityCheckerPlugin).toHaveBeenCalledTimes(0);
+    });
+
+    test('should listen for network change to online', async () => {
+      jest.useFakeTimers();
+      const addEventListenerMock = jest.spyOn(window, 'addEventListener');
+      const flush = jest.spyOn(client, 'flush').mockReturnValue({ promise: Promise.resolve() });
+
+      await client.init(apiKey, {
+        defaultTracking: false,
+      }).promise;
+      window.dispatchEvent(new Event('online'));
+
+      expect(addEventListenerMock).toHaveBeenCalledWith('online', expect.any(Function));
+      expect(client.config.offline).toBe(false);
+
+      jest.advanceTimersByTime(client.config.flushIntervalMillis);
+      expect(flush).toHaveBeenCalledTimes(1);
+
+      jest.useRealTimers();
+      addEventListenerMock.mockRestore();
+      flush.mockRestore();
+    });
+
+    test('should listen for network change to offline', async () => {
+      jest.useFakeTimers();
+      const addEventListenerMock = jest.spyOn(window, 'addEventListener');
+
+      await client.init(apiKey, {
+        defaultTracking: false,
+      }).promise;
+      expect(client.config.offline).toBe(false);
+
+      window.dispatchEvent(new Event('offline'));
+      expect(addEventListenerMock).toHaveBeenCalledWith('offline', expect.any(Function));
+      expect(client.config.offline).toBe(true);
+
+      jest.useRealTimers();
+      addEventListenerMock.mockRestore();
+    });
+
+    test('should not support offline mode if global scope returns undefined', async () => {
+      const getGlobalScopeMock = jest.spyOn(AnalyticsClientCommon, 'getGlobalScope').mockReturnValueOnce(undefined);
+      const addEventListenerMock = jest.spyOn(window, 'addEventListener');
+
+      await client.init(apiKey, {
+        defaultTracking: false,
+      }).promise;
+
+      window.dispatchEvent(new Event('online'));
+      expect(client.config.offline).toBe(false);
+
+      client.config.offline = true;
+      window.dispatchEvent(new Event('offline'));
+      expect(client.config.offline).toBe(true);
+
+      getGlobalScopeMock.mockRestore();
+      addEventListenerMock.mockRestore();
+    });
   });
 
   describe('getUserId', () => {

packages/analytics-browser/test/config.test.ts

@@ -58,6 +58,7 @@ describe('config', () => {
         loggerProvider: logger,
         logLevel: LogLevel.Warn,
         minIdLength: undefined,
+        offline: false,
         partnerId: undefined,
         plan: undefined,
         ingestionMetadata: undefined,
@@ -113,6 +114,7 @@ describe('config', () => {
         loggerProvider: logger,
         logLevel: LogLevel.Warn,
         minIdLength: undefined,
+        offline: false,
         partnerId: undefined,
         plan: undefined,
         ingestionMetadata: undefined,
@@ -165,6 +167,7 @@ describe('config', () => {
             upgrade: false,
           },
           defaultTracking: true,
+          offline: true,
         },
         new AmplitudeBrowser(),
       );
@@ -197,6 +200,7 @@ describe('config', () => {
         logLevel: 2,
         loggerProvider: logger,
         minIdLength: undefined,
+        offline: true,
         partnerId: 'partnerId',
         plan: {
           version: '0',

packages/analytics-browser/test/helpers/mock.ts

@@ -37,6 +37,7 @@ export const createConfigurationMock = (options?: Partial<BrowserConfig>) => {
     logLevel: LogLevel.Warn,
     loggerProvider: new Logger(),
     minIdLength: undefined,
+    offline: false,
     optOut: false,
     plan: undefined,
     ingestionMetadata: undefined,

packages/analytics-browser/test/plugins/network-connectivity-checker.test.ts

@@ -0,0 +1,46 @@
+/* eslint-disable @typescript-eslint/unbound-method */
+
+import { createAmplitudeMock, createConfigurationMock } from '../helpers/mock';
+import { networkConnectivityCheckerPlugin } from '../../src/plugins/network-connectivity-checker';
+
+describe('networkConnectivityCheckerPlugin', () => {
+  const amplitude = createAmplitudeMock();
+  const config = createConfigurationMock();
+
+  test('should set up correctly when online', async () => {
+    const plugin = networkConnectivityCheckerPlugin();
+    jest.spyOn(navigator, 'onLine', 'get').mockReturnValue(true);
+    const addEventListenerSpy = jest.spyOn(window, 'addEventListener');
+
+    await plugin.setup?.(config, amplitude);
+
+    expect(config.offline).toEqual(false);
+    expect(addEventListenerSpy).toHaveBeenCalledWith('online', expect.any(Function));
+    expect(addEventListenerSpy).toHaveBeenCalledWith('offline', expect.any(Function));
+    addEventListenerSpy.mockRestore();
+  });
+
+  test('should set up correctly when offline', async () => {
+    const plugin = networkConnectivityCheckerPlugin();
+    jest.spyOn(navigator, 'onLine', 'get').mockReturnValue(false);
+    const addEventListenerSpy = jest.spyOn(window, 'addEventListener');
+
+    await plugin.setup?.(config, amplitude);
+
+    expect(config.offline).toEqual(true);
+    expect(addEventListenerSpy).toHaveBeenCalledWith('online', expect.any(Function));
+    expect(addEventListenerSpy).toHaveBeenCalledWith('offline', expect.any(Function));
+    addEventListenerSpy.mockRestore();
+  });
+
+  test('should teardown plugin', async () => {
+    const plugin = networkConnectivityCheckerPlugin();
+    const removeEventListenerSpy = jest.spyOn(window, 'removeEventListener');
+
+    await plugin.setup?.(createConfigurationMock(), amplitude);
+    await plugin.teardown?.();
+
+    expect(removeEventListenerSpy).toHaveBeenCalledWith('online', expect.any(Function));
+    expect(removeEventListenerSpy).toHaveBeenCalledWith('offline', expect.any(Function));
+  });
+});

packages/analytics-core/src/config.ts

@@ -26,6 +26,7 @@ export const getDefaultConfig = () => ({
   instanceName: '$default_instance',
   logLevel: LogLevel.Warn,
   loggerProvider: new Logger(),
+  offline: false,
   optOut: false,
   serverUrl: AMPLITUDE_SERVER_URL,
   serverZone: 'US' as ServerZoneType,
@@ -41,6 +42,7 @@ export class Config implements IConfig {
   loggerProvider: ILogger;
   logLevel: LogLevel;
   minIdLength?: number;
+  offline?: boolean | null;
   plan?: Plan;
   ingestionMetadata?: IngestionMetadata;
   serverUrl: string | undefined;
@@ -69,6 +71,7 @@ export class Config implements IConfig {
     this.minIdLength = options.minIdLength;
     this.plan = options.plan;
     this.ingestionMetadata = options.ingestionMetadata;
+    this.offline = options.offline !== undefined ? options.offline : defaultConfig.offline;
     this.optOut = options.optOut ?? defaultConfig.optOut;
     this.serverUrl = options.serverUrl;
     this.serverZone = options.serverZone || defaultConfig.serverZone;

packages/analytics-core/src/plugins/destination.ts

@@ -106,7 +106,10 @@ export class Destination implements DestinationPlugin {
   }
 
   schedule(timeout: number) {
-    if (this.scheduled) return;
+    if (this.scheduled || this.config.offline) {
+      return;
+    }
+
     this.scheduled = setTimeout(() => {
       void this.flush(true).then(() => {
         if (this.queue.length > 0) {
@@ -117,6 +120,11 @@ export class Destination implements DestinationPlugin {
   }
 
   async flush(useRetry = false) {
+    // Skip flush if offline
+    if (this.config.offline) {
+      return;
+    }
+
     const list: Context[] = [];
     const later: Context[] = [];
     this.queue.forEach((context) => (context.timeout === 0 ? list.push(context) : later.push(context)));

packages/analytics-core/test/config.test.ts

@@ -26,6 +26,7 @@ describe('config', () => {
       logLevel: LogLevel.Warn,
       loggerProvider: new Logger(),
       minIdLength: undefined,
+      offline: false,
       _optOut: false, // private for `optOut` getter/setter
       partnerId: undefined,
       plan: undefined,
@@ -44,6 +45,7 @@ describe('config', () => {
     const config = new Config({
       apiKey: API_KEY,
       logLevel: LogLevel.Verbose,
+      offline: true,
       optOut: true,
       plan: { version: '0' },
       ingestionMetadata: {
@@ -63,6 +65,7 @@ describe('config', () => {
       logLevel: LogLevel.Verbose,
       loggerProvider: new Logger(),
       minIdLength: undefined,
+      offline: true,
       _optOut: true,
       plan: {
         version: '0',