fix: multiple same-event "once" listeners should all be called (#16)

Co-authored-by: Artem Zakharchenko <[email protected]>

src/Emitter.ts

@@ -56,7 +56,9 @@ export class Emitter<Events extends EventMap> {
   private _getListeners<EventName extends keyof Events>(
     eventName: EventName
   ): Array<Listener<Array<unknown>>> {
-    return this.events.get(eventName) || []
+    // Always return a copy of the listeners array
+    // so they are fixed at the time of the "_getListeners" call.
+    return Array.prototype.concat.apply([], this.events.get(eventName)) || []
   }
 
   private _removeListener<EventName extends keyof Events>(
@@ -81,6 +83,9 @@ export class Emitter<Events extends EventMap> {
       listener.apply(this, data)
     }
 
+    // Inherit the name of the original listener.
+    Object.defineProperty(onceListener, 'name', { value: listener.name })
+
     return onceListener
   }
 

test/Emitter/once.test.ts

@@ -36,3 +36,27 @@ it('can have multiple once listeners for different events', () => {
   expect(emitter.listenerCount('hello')).toBe(0)
   expect(emitter.listenerCount('goodbye')).toBe(0)
 })
+
+it('emits multiple "once" event of the same name', () => {
+  const emitter = new Emitter<Events>()
+  const firstHelloListener = jest.fn()
+  const secondHelloListener = jest.fn()
+
+  Object.defineProperty(firstHelloListener, 'name', {
+    value: 'firstHelloListener',
+  })
+  Object.defineProperty(secondHelloListener, 'name', {
+    value: 'secondHelloListener',
+  })
+
+  emitter.once('hello', firstHelloListener)
+  emitter.once('hello', secondHelloListener)
+
+  emitter.emit('hello', 'John')
+
+  expect(firstHelloListener).toHaveBeenCalledTimes(1)
+  expect(firstHelloListener).toHaveBeenCalledWith('John')
+
+  expect(secondHelloListener).toHaveBeenCalledTimes(1)
+  expect(secondHelloListener).toHaveBeenCalledWith('John')
+})