Add off callback to EventEmitter on methods

packages/stack/src/utils/event-emitter.ts

@@ -11,6 +11,8 @@ interface ListenerEntry<T> {
   once?: boolean;
 }
 
+export type OffCallback = () => void;
+
 export class EventEmitter<T extends EventMap> {
   private listeners: Map<keyof T, Set<ListenerEntry<T[keyof T]>>> = new Map();
 
@@ -18,7 +20,7 @@ export class EventEmitter<T extends EventMap> {
     type: K,
     listener: Listener<T[K]>,
     debounceMilliseconds?: number,
-  ): Listener<T[K]> {
+  ): OffCallback {
     const wrappedListener =
       debounceMilliseconds && debounceMilliseconds > 0
         ? this.debounce(listener, debounceMilliseconds)
@@ -35,14 +37,16 @@ export class EventEmitter<T extends EventMap> {
     };
 
     this.listeners.get(type)?.add(listenerEntry as ListenerEntry<T[keyof T]>);
-    return listener;
+
+    // Return an "off" callback that can be called to stop listening for events.
+    return () => this.off(type, listener);
   }
 
   once<K extends keyof T>(
     type: K,
     listener: Listener<T[K]>,
     debounceMilliseconds?: number,
-  ): Listener<T[K]> {
+  ): OffCallback {
     const wrappedListener: Listener<T[K]> = (detail: T[K]) => {
       this.off(type, listener);
       listener(detail);
@@ -65,7 +69,9 @@ export class EventEmitter<T extends EventMap> {
     };
 
     this.listeners.get(type)?.add(listenerEntry as ListenerEntry<T[keyof T]>);
-    return listener;
+
+    // Return an "off" callback that can be called to stop listening for events.
+    return () => this.off(type, listener);
   }
 
   off<K extends keyof T>(type: K, listener: Listener<T[K]>): void {