fix(core): correctly check if an event has any listeners bound to it (#1935)

bcakmakoglu · web-flow · commit ca54587962af · 2025-08-28T08:50:19.000+02:00
* fix(core): separate listeners from emitter for correct check on hasListeners

Signed-off-by: braks &lt;78412429+bcakmakoglu@users.noreply.github.com&gt;

* fix(core): check for listeners bound via emits

Signed-off-by: braks &lt;78412429+bcakmakoglu@users.noreply.github.com&gt;

* chore(changeset): add

---------

Signed-off-by: braks &lt;78412429+bcakmakoglu@users.noreply.github.com&gt;
diff --git a/.changeset/neat-days-learn.md b/.changeset/neat-days-learn.md
@@ -0,0 +1,5 @@
+---
+"@vue-flow/core": patch
+---
+
+Correctly check if an event listener was bound to the VueFlow component, using for example `@node-click` or if a listener was bound using the exposed event hooks from `useVueFlow` when determening if a listener for an event exists at all.
diff --git a/packages/core/src/container/VueFlow/VueFlow.vue b/packages/core/src/container/VueFlow/VueFlow.vue
@@ -56,12 +56,12 @@ const modelValue = useVModel(props, 'modelValue', emit)
 const modelNodes = useVModel(props, 'nodes', emit)
 const modelEdges = useVModel(props, 'edges', emit)
 
-const instance = useVueFlow(props)
+const vfInstance = useVueFlow(props)
 
 // watch props and update store state
-const dispose = useWatchProps({ modelValue, nodes: modelNodes, edges: modelEdges }, props, instance)
+const disposeWatchers = useWatchProps({ modelValue, nodes: modelNodes, edges: modelEdges }, props, vfInstance)
 
-useHooks(emit, instance.hooks)
+useHooks(emit, vfInstance.hooks)
 
 useOnInitHandler()
 
@@ -72,12 +72,9 @@ useStylesLoadedWarning()
 // as that would require a lot of boilerplate and causes significant performance drops
 provide(Slots, slots)
 
-onUnmounted(() => {
-  // clean up watcher scope
-  dispose()
-})
+onUnmounted(disposeWatchers)
 
-defineExpose<VueFlowStore>(instance)
+defineExpose<VueFlowStore>(vfInstance)
 </script>
 
 <script lang="ts">
@@ -88,7 +85,7 @@ export default {
 </script>
 
 <template>
-  <div :ref="instance.vueFlowRef" class="vue-flow">
+  <div :ref="vfInstance.vueFlowRef" class="vue-flow">
     <Viewport>
       <EdgeRenderer />
 
diff --git a/packages/core/src/store/hooks.ts b/packages/core/src/store/hooks.ts
@@ -1,10 +1,9 @@
 import { tryOnScopeDispose } from '@vueuse/core'
 import type { Ref } from 'vue'
-import { onBeforeMount } from 'vue'
-import type { FlowHooks } from '../types'
+import { getCurrentInstance, onBeforeMount } from 'vue'
+import type { FlowEvents, FlowHooks } from '../types'
 import { createExtendedEventHook, warn } from '../utils'
 
-// flow event hooks
 export function createHooks(): FlowHooks {
   return {
     edgesChange: createExtendedEventHook(),
@@ -64,18 +63,40 @@ export function createHooks(): FlowHooks {
 }
 
 export function useHooks(emit: (...args: any[]) => void, hooks: Ref<FlowHooks>) {
+  const inst = getCurrentInstance()
+
   onBeforeMount(() => {
     for (const [key, value] of Object.entries(hooks.value)) {
-      const listener = (data: any) => {
+      const listener = (data: unknown) => {
         emit(key, data)
       }
 
-      // push into fns instead of using `on` to avoid overwriting default handlers - the emits should be called in addition to the default handlers
-      value.fns.add(listener)
+      // push into fns instead of using `on` to avoid overwriting default handlers - the emitter should be called in addition to the default handlers
+      value.setEmitter(listener)
+      tryOnScopeDispose(value.removeEmitter)
 
-      tryOnScopeDispose(() => {
-        value.off(listener)
-      })
+      value.setHasEmitListeners(() => hasVNodeListener(key as keyof FlowEvents))
+      tryOnScopeDispose(value.removeHasEmitListeners)
     }
   })
+
+  function hasVNodeListener(event: keyof FlowEvents) {
+    const key = toHandlerKey(event)
+    // listeners live on vnode.props; value can be a Function or an array of Functions
+    const h = inst?.vnode.props?.[key]
+    return !!h
+  }
+}
+
+/**
+ * Converts an event name to the corresponding handler key.
+ * E.g. 'nodeClick' -> 'onNodeClick'
+ *
+ * @param event The event name to convert.
+ * @returns The corresponding handler key.
+ */
+function toHandlerKey(event: string) {
+  const [head, ...rest] = event.split(':')
+  const camel = head.replace(/(?:^|-)(\w)/g, (_, c: string) => c.toUpperCase())
+  return `on${camel}${rest.length ? `:${rest.join(':')}` : ''}`
 }
diff --git a/packages/core/src/utils/createExtendedEventHook.ts b/packages/core/src/utils/createExtendedEventHook.ts
@@ -1,63 +1,89 @@
 import type { EventHook } from '@vueuse/core'
 import { tryOnScopeDispose } from '@vueuse/core'
 
-/**
- * Source code taken from https://github.com/vueuse/vueuse/blob/main/packages/shared/createEventHook/index.ts
- *
- * Modified to be able to check if there are any event listeners
- */
 export interface EventHookExtended<T> extends EventHook<T> {
+  /** true if any user listeners are registered (emitter ignored) */
   hasListeners: () => boolean
-  fns: Set<(param: T) => void>
+  /** current user listeners (read-only; do not mutate externally) */
+  listeners: ReadonlySet<(param: T) => void>
+  /** wire a single external emitter (e.g., for `emit`) */
+  setEmitter: (fn: (param: T) => void) => void
+  /** remove the external emitter */
+  removeEmitter: () => void
+  /** wire a function to detect if any emit listeners exist (e.g., for `$listeners` in Vue 2) */
+  setHasEmitListeners: (fn: () => boolean) => void
+  /** remove the emit listeners detector */
+  removeHasEmitListeners: () => void
 }
 
-export function createExtendedEventHook<T = any>(defaultHandler?: (param: T) => void): EventHookExtended<T> {
-  const fns = new Set<(param: T) => void>()
+type Handler<T = any> = (param: T) => any | Promise<any>
+
+const noop: Handler = () => {}
 
-  let hasDefaultHandler = false
+export function createExtendedEventHook<T = any>(defaultHandler?: (param: T) => void): EventHookExtended<T> {
+  const listeners = new Set<Handler>()
+  let emitter: Handler = noop
+  let hasEmitListeners = () => false
 
-  const hasListeners = () => fns.size > 0
+  const hasListeners = () => listeners.size > 0 || hasEmitListeners()
 
-  if (defaultHandler) {
-    hasDefaultHandler = true
-    fns.add(defaultHandler)
+  const setEmitter = (fn: Handler) => {
+    emitter = fn
   }
 
-  const off = (fn: (param: T) => void) => {
-    fns.delete(fn)
+  const removeEmitter = () => {
+    emitter = noop
   }
 
-  const on = (fn: (param: T) => void) => {
-    if (defaultHandler && hasDefaultHandler) {
-      fns.delete(defaultHandler)
-    }
+  const setHasEmitListeners = (fn: () => boolean) => {
+    hasEmitListeners = fn
+  }
 
-    fns.add(fn)
+  const removeHasEmitListeners = () => {
+    hasEmitListeners = () => false
+  }
 
-    const offFn = () => {
-      off(fn)
+  const off = (fn: Handler) => {
+    listeners.delete(fn)
+  }
 
-      if (defaultHandler && hasDefaultHandler) {
-        fns.add(defaultHandler)
-      }
-    }
+  const on = (fn: Handler) => {
+    listeners.add(fn)
 
+    const offFn = () => off(fn)
     tryOnScopeDispose(offFn)
 
-    return {
-      off: offFn,
-    }
+    return { off: offFn }
   }
 
+  /**
+   * Trigger order:
+   * 1) If any user listeners OR an emitter exist -> call all of those (defaultHandler is skipped)
+   * 2) Else (no listeners and no emitter) -> call defaultHandler (if provided)
+   *
+   * Errors are isolated via allSettled so one failing handler doesn't break others.
+   */
   const trigger = (param: T) => {
-    return Promise.all(Array.from(fns).map((fn) => fn(param)))
+    const queue: Handler[] = [emitter]
+
+    if (hasListeners()) {
+      queue.push(...listeners)
+    } else if (defaultHandler) {
+      queue.push(defaultHandler)
+    }
+
+    return Promise.allSettled(queue.map((fn) => fn(param)))
   }
 
   return {
     on,
     off,
     trigger,
     hasListeners,
-    fns,
+    listeners,
+    setEmitter,
+    removeEmitter,
+    setHasEmitListeners,
+    removeHasEmitListeners,
   }
 }

-Original file line number
+Diff line change
@@ @@ -0,0 +1,5 @@ @@
 +---
 +"@vue-flow/core": patch
 +---
++
 +Correctly check if an event listener was bound to the VueFlow component, using for example `@node-click` or if a listener was bound using the exposed event hooks from `useVueFlow` when determening if a listener for an event exists at all.