feat: Remove event target shim. (#545)

Unlike the EventEmitter in the node SDK the EventTarget was not
providing an interface directly on the LDClient. The LDClient has its
own off/on interface which is not directly implemented via an event
target. Which means removing it simplifies the implementation instead of
complicating it.

Second it is in the common code and node in a leaf implementation. Which
means it requires a polyfill where it is not supported. Like when using
hermes with React Native.

Typically we dispatch using a micro-task, but EventTarget dispatches
synchronously. For now this maintains the synchronous behavior.

Fixes: #412

packages/sdk/react-native/package.json

@@ -45,8 +45,7 @@
   "dependencies": {
     "@launchdarkly/js-client-sdk-common": "1.3.0",
     "@react-native-async-storage/async-storage": "^1.21.0",
-    "base64-js": "^1.5.1",
-    "event-target-shim": "^6.0.2"
+    "base64-js": "^1.5.1"
   },
   "devDependencies": {
     "@launchdarkly/private-js-mocks": "0.0.1",

packages/sdk/react-native/src/index.ts

@@ -5,12 +5,9 @@
  *
  * @packageDocumentation
  */
-import { setupPolyfill } from './polyfills';
 import ReactNativeLDClient from './ReactNativeLDClient';
 import RNOptions from './RNOptions';
 
-setupPolyfill();
-
 export * from '@launchdarkly/js-client-sdk-common';
 
 export * from './hooks';

packages/sdk/react-native/src/polyfills/index.ts

@@ -1,13 +1,4 @@
-import EventTarget from 'event-target-shim';
-
 import { type Hasher, sha256 } from '../fromExternal/js-sha256';
 import { base64FromByteArray, btoa } from './btoa';
-import CustomEvent from './CustomEvent';
 
-function setupPolyfill() {
-  Object.assign(global, {
-    EventTarget,
-    CustomEvent,
-  });
-}
-export { base64FromByteArray, btoa, type Hasher, setupPolyfill, sha256 };
+export { base64FromByteArray, btoa, type Hasher, sha256 };

packages/shared/sdk-client/src/api/LDEmitter.test.ts

@@ -1,14 +1,21 @@
-import { LDContext } from '@launchdarkly/js-sdk-common';
+import { LDContext, LDLogger } from '@launchdarkly/js-sdk-common';
 
 import LDEmitter from './LDEmitter';
 
 describe('LDEmitter', () => {
   const error = { type: 'network', message: 'unreachable' };
   let emitter: LDEmitter;
+  let logger: LDLogger;
 
   beforeEach(() => {
     jest.resetAllMocks();
-    emitter = new LDEmitter();
+    logger = {
+      debug: jest.fn(),
+      info: jest.fn(),
+      warn: jest.fn(),
+      error: jest.fn(),
+    };
+    emitter = new LDEmitter(logger);
   });
 
   test('subscribe and handle', () => {
@@ -77,12 +84,13 @@ describe('LDEmitter', () => {
 
   test('on listener with arguments', () => {
     const context = { kind: 'user', key: 'test-user-1' };
-    const onListener = jest.fn((c: LDContext) => c);
+    const arg2 = { test: 'test' };
+    const onListener = jest.fn((c: LDContext, a2: any) => [c, a2]);
 
     emitter.on('change', onListener);
-    emitter.emit('change', context);
+    emitter.emit('change', context, arg2);
 
-    expect(onListener).toBeCalledWith(context);
+    expect(onListener).toBeCalledWith(context, arg2);
   });
 
   test('unsubscribe one of many listeners', () => {
@@ -131,4 +139,15 @@ describe('LDEmitter', () => {
     expect(errorHandler1).not.toBeCalled();
     expect(errorHandler2).not.toBeCalled();
   });
+
+  it('handles errors generated by the callback', () => {
+    emitter.on('error', () => {
+      throw new Error('toast');
+    });
+    // Should not have an uncaught exception.
+    emitter.emit('error');
+    expect(logger.error).toHaveBeenCalledWith(
+      'Encountered error invoking handler for "error", detail: "Error: toast"',
+    );
+  });
 });

packages/shared/sdk-client/src/api/LDEmitter.ts

@@ -1,53 +1,20 @@
+import { LDLogger } from '@launchdarkly/js-sdk-common';
+
 export type EventName = 'error' | 'change';
 
-type CustomEventListeners = {
-  original: Function;
-  custom: Function;
-};
-/**
- * Native api usage: EventTarget.
- *
- * This is an event emitter using the standard built-in EventTarget web api.
- * https://developer.mozilla.org/en-US/docs/Web/API/EventTarget
- *
- * In react-native use event-target-shim to polyfill EventTarget. This is safe
- * because the react-native repo uses it too.
- * https://github.com/mysticatea/event-target-shim
- */
 export default class LDEmitter {
-  private et: EventTarget = new EventTarget();
+  private listeners: Map<EventName, Function[]> = new Map();
 
-  private listeners: Map<EventName, CustomEventListeners[]> = new Map();
+  constructor(private logger?: LDLogger) {}
 
-  /**
-   * Cache all listeners in a Map so we can remove them later
-   * @param name string event name
-   * @param originalListener pointer to the original function as specified by
-   * the consumer
-   * @param customListener pointer to the custom function based on original
-   * listener. This is needed to allow for CustomEvents.
-   * @private
-   */
-  private saveListener(name: EventName, originalListener: Function, customListener: Function) {
-    const listener = { original: originalListener, custom: customListener };
+  on(name: EventName, listener: Function) {
     if (!this.listeners.has(name)) {
       this.listeners.set(name, [listener]);
     } else {
       this.listeners.get(name)?.push(listener);
     }
   }
 
-  on(name: EventName, listener: Function) {
-    const customListener = (e: Event) => {
-      const { detail } = e as CustomEvent;
-
-      // invoke listener with args from CustomEvent
-      listener(...detail);
-    };
-    this.saveListener(name, listener, customListener);
-    this.et.addEventListener(name, customListener);
-  }
-
   /**
    * Unsubscribe one or all events.
    *
@@ -61,11 +28,8 @@ export default class LDEmitter {
     }
 
     if (listener) {
-      const toBeRemoved = existingListeners.find((c) => c.original === listener);
-      this.et.removeEventListener(name, toBeRemoved?.custom as any);
-
       // remove from internal cache
-      const updated = existingListeners.filter((l) => l.original !== listener);
+      const updated = existingListeners.filter((fn) => fn !== listener);
       if (updated.length === 0) {
         this.listeners.delete(name);
       } else {
@@ -74,15 +38,21 @@ export default class LDEmitter {
       return;
     }
 
-    // remove all listeners
-    existingListeners.forEach((l) => {
-      this.et.removeEventListener(name, l.custom as any);
-    });
+    // listener was not specified, so remove them all for that event
     this.listeners.delete(name);
   }
 
+  private invokeListener(listener: Function, name: EventName, ...detail: any[]) {
+    try {
+      listener(...detail);
+    } catch (err) {
+      this.logger?.error(`Encountered error invoking handler for "${name}", detail: "${err}"`);
+    }
+  }
+
   emit(name: EventName, ...detail: any[]) {
-    this.et.dispatchEvent(new CustomEvent(name, { detail }));
+    const listeners = this.listeners.get(name);
+    listeners?.forEach((listener) => this.invokeListener(listener, name, ...detail));
   }
 
   eventNames(): string[] {