feat: use EvenEmitter3 for web-sdk (#847)

<!-- Please use this template for your pull request. -->
<!-- Please use the sections that you need and delete other sections -->

## This PR
<!-- add the description of the PR here -->

Fixes an issue where the `events` node polyfill does not comply to the
`node:events` types.
When trying to use the web OpenFeatureEventEmitter the following error
message comes up, describing that the `events` polyfill's EventEmitter
is incompatible to `node:events` EventEmitter.

```
✘ [ERROR] TS2416: Property 'eventEmitter' in type 'OpenFeatureEventEmitter' is not assignable to the same property in base type 'GenericEventEmitter<ProviderEmittableEvents, Record<string, unknown>>'.
  Type 'EventEmitter' is not assignable to type 'PlatformEventEmitter'.
    Types of property 'addListener' are incompatible.
      Type '(type: string | number, listener: Listener) => EventEmitter' is not assignable to type '(eventName: string | symbol, listener: (...args: any[]) => void) => PlatformEventEmitter'.
        Types of parameters 'type' and 'eventName' are incompatible.
          Type 'string | symbol' is not assignable to type 'string | number'.
            Type 'symbol' is not assignable to type 'string | number'.
```

This PR fixes that issue by not using the `events` anymore and instead
using https://www.npmjs.com/package/eventemitter3

cc @toddbaert 

### Related Issues
<!-- add here the GitHub issue that this PR resolves if applicable -->

Fixes #845

---------

Signed-off-by: Lukas Reining <[email protected]>
Signed-off-by: Todd Baert <[email protected]>
Co-authored-by: Todd Baert <[email protected]>

Author: lukas-reining

package-lock.json

@@ -37,7 +37,6 @@
   },
   "devDependencies": {
     "@rollup/plugin-typescript": "^11.1.6",
-    "@types/events": "^3.0.3",
     "@types/jest": "^29.5.12",
     "@types/node": "^20.11.16",
     "@types/react": "^18.2.55",
@@ -51,7 +50,7 @@
     "eslint-plugin-import": "^2.29.1",
     "eslint-plugin-jest": "^27.6.3",
     "eslint-plugin-jsdoc": "^48.0.6",
-    "events": "^3.3.0",
+    "eventemitter3": "^5.0.1",
     "jest": "^29.7.0",
     "jest-config": "^29.7.0",
     "jest-cucumber": "^3.0.1",
@@ -76,4 +75,4 @@
     "packages/react",
     "packages/nest"
   ]
-}
+}

package.json

@@ -1,6 +1,7 @@
 import { GenericEventEmitter } from '@openfeature/core';
-import { EventEmitter } from 'events';
+import { EventEmitter } from 'eventemitter3';
 import { ProviderEmittableEvents } from './events';
+
 /**
  * The OpenFeatureEventEmitter can be used by provider developers to emit
  * events at various parts of the provider lifecycle.
@@ -9,12 +10,9 @@ import { ProviderEmittableEvents } from './events';
  * the result of the initialize method.
  */
 export class OpenFeatureEventEmitter extends GenericEventEmitter<ProviderEmittableEvents> {
-  protected readonly eventEmitter = new EventEmitter({ captureRejections: true });
+  protected readonly eventEmitter = new EventEmitter();
 
   constructor() {
     super();
-    this.eventEmitter.on('error', (err) => {
-      this._logger?.error('Error running event handler:', err);
-    });
   }
 }

packages/client/src/events/open-feature-event-emitter.ts

@@ -7,12 +7,15 @@ import { AllProviderEvents, AnyProviderEvent } from './events';
  * The GenericEventEmitter should only be used within the SDK. It supports additional properties that can be included
  * in the event details.
  */
-export abstract class GenericEventEmitter<E extends AnyProviderEvent, AdditionalContext extends Record<string, unknown> = Record<string, unknown>>
+export abstract class GenericEventEmitter<
+    E extends AnyProviderEvent,
+    AdditionalContext extends Record<string, unknown> = Record<string, unknown>,
+  >
   implements ProviderEventEmitter<E>, ManageLogger<GenericEventEmitter<E, AdditionalContext>>
 {
   protected abstract readonly eventEmitter: PlatformEventEmitter;
 
-  private readonly _handlers: { [key in AnyProviderEvent]: WeakMap<EventHandler, EventHandler[]>} = {
+  private readonly _handlers: { [key in AnyProviderEvent]: WeakMap<EventHandler, EventHandler[]> } = {
     [AllProviderEvents.ConfigurationChanged]: new WeakMap<EventHandler, EventHandler[]>(),
     [AllProviderEvents.ContextChanged]: new WeakMap<EventHandler, EventHandler[]>(),
     [AllProviderEvents.Ready]: new WeakMap<EventHandler, EventHandler[]>(),
@@ -33,7 +36,11 @@ export abstract class GenericEventEmitter<E extends AnyProviderEvent, Additional
     // The handlers have to be wrapped with an async function because if a synchronous functions throws an error,
     // the other handlers will not run.
     const asyncHandler = async (details?: EventDetails) => {
-      await handler(details);    
+      try {
+        await handler(details);
+      } catch (err) {
+        this._logger?.error('Error running event handler:', err);
+      }
     };
     // The async handler has to be written to the map, because we need to get the wrapper function when deleting a listener
     const existingAsyncHandlers = this._handlers[eventType].get(handler);
@@ -84,7 +91,7 @@ export abstract class GenericEventEmitter<E extends AnyProviderEvent, Additional
  * This is an un-exported type that corresponds to NodeJS.EventEmitter.
  * We can't use that type here, because this module is used in both the browser, and the server.
  * In the server, node (or whatever server runtime) provides an implementation for this.
- * In the browser, we bundle in the popular 'events' package, which is a polyfill of NodeJS.EventEmitter.
+ * In the browser, we bundle in the popular 'EventEmitter3' package, which is a polyfill of NodeJS.EventEmitter.
  */
 /* eslint-disable */
 interface PlatformEventEmitter {
@@ -94,13 +101,8 @@ interface PlatformEventEmitter {
   removeListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
   off(eventName: string | symbol, listener: (...args: any[]) => void): this;
   removeAllListeners(event?: string | symbol): this;
-  setMaxListeners(n: number): this;
-  getMaxListeners(): number;
   listeners(eventName: string | symbol): Function[];
-  rawListeners(eventName: string | symbol): Function[];
   emit(eventName: string | symbol, ...args: any[]): boolean;
   listenerCount(eventName: string | symbol, listener?: Function): number;
-  prependListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
-  prependOnceListener(eventName: string | symbol, listener: (...args: any[]) => void): this;
   eventNames(): Array<string | symbol>;
-}
+}