Clear dangling EventListeners and Detached Nodes when a controller is removed from the DOM

src/core/binding_observer.ts

@@ -7,7 +7,7 @@ import { Token, ValueListObserver, ValueListObserverDelegate } from "../mutation
 
 export interface BindingObserverDelegate extends ErrorHandler {
   bindingConnected(binding: Binding): void
-  bindingDisconnected(binding: Binding): void
+  bindingDisconnected(binding: Binding, clearEventListeners?: boolean): void
 }
 
 export class BindingObserver implements ValueListObserverDelegate<Action> {
@@ -72,7 +72,7 @@ export class BindingObserver implements ValueListObserverDelegate<Action> {
   }
 
   private disconnectAllActions() {
-    this.bindings.forEach((binding) => this.delegate.bindingDisconnected(binding))
+    this.bindings.forEach((binding) => this.delegate.bindingDisconnected(binding, true))
     this.bindingsByAction.clear()
   }
 

src/core/dispatcher.ts

@@ -41,8 +41,9 @@ export class Dispatcher implements BindingObserverDelegate {
     this.fetchEventListenerForBinding(binding).bindingConnected(binding)
   }
 
-  bindingDisconnected(binding: Binding) {
+  bindingDisconnected(binding: Binding, clearEventListeners: boolean = false) {
     this.fetchEventListenerForBinding(binding).bindingDisconnected(binding)
+    if (clearEventListeners) this.clearEventListenersForBinding(binding)
   }
 
   // Error handling
@@ -51,6 +52,23 @@ export class Dispatcher implements BindingObserverDelegate {
     this.application.handleError(error, `Error ${message}`, detail)
   }
 
+  private clearEventListenersForBinding(binding: Binding) {
+    const eventListener = this.fetchEventListenerForBinding(binding)
+    if (!eventListener.hasBindings()) {
+      eventListener.disconnect()
+      this.removeMappedEventListenerFor(binding)
+    }
+  }
+
+  private removeMappedEventListenerFor(binding: Binding) {
+    const { eventTarget, eventName, eventOptions } = binding
+    const eventListenerMap = this.fetchEventListenerMapForEventTarget(eventTarget)
+    const cacheKey = this.cacheKey(eventName, eventOptions)
+
+    eventListenerMap.delete(cacheKey)
+    if (eventListenerMap.size == 0) this.eventListenerMaps.delete(eventTarget)
+  }
+
   private fetchEventListenerForBinding(binding: Binding): EventListener {
     const { eventTarget, eventName, eventOptions } = binding
     return this.fetchEventListener(eventTarget, eventName, eventOptions)

src/core/event_listener.ts

@@ -43,6 +43,10 @@ export class EventListener implements EventListenerObject {
     }
   }
 
+  hasBindings() {
+    return this.unorderedBindings.size > 0
+  }
+
   get bindings(): Binding[] {
     return Array.from(this.unorderedBindings).sort((left, right) => {
       const leftIndex = left.index,

src/tests/modules/core/memory_tests.ts

@@ -0,0 +1,22 @@
+import { ControllerTestCase } from "../../cases/controller_test_case"
+
+export default class MemoryTests extends ControllerTestCase() {
+  controllerElement!: Element
+
+  async setup() {
+    this.controllerElement = this.controller.element
+  }
+
+  fixtureHTML = `
+    <div data-controller="${this.identifier}">
+      <button data-action="${this.identifier}#doLog">Log</button>
+      <button data-action="${this.identifier}#doAlert">Alert</button>
+    </div>
+  `
+
+  async "test removing a controller clears dangling eventListeners"() {
+    this.assert.equal(this.application.dispatcher.eventListeners.length, 2)
+    await this.fixtureElement.removeChild(this.controllerElement)
+    this.assert.equal(this.application.dispatcher.eventListeners.length, 0)
+  }
+}