Check if a component has an event listener attached to it

Question

When there are listeners attached to a component they are available in the $listeners property of the component.

You can use that property to determine if a specific listener is available. For example, here is a computed property that checks for the existence of a cancel listener.

computed:{
  hasCancelListener(){
    return this.$listeners && this.$listeners.cancel
  }
}

And here is an example of that used in a component.

console.clear()

Vue.component("CustomForm", {
  template:`
    <div>
      <h1>Custom Form</h1>
      <button v-if="hasCancelListener" @click="$emit('cancel')">I have a listener!</button>
    </div>
  `,
  computed:{
    hasCancelListener(){
      return this.$listeners && this.$listeners.cancel
    }
  },
})

new Vue({
  el: "#app",
  methods:{
    onCancel(){
      alert('canceled')
    }
  }
})

<script src="https://unpkg.com/vue@2.4.2"></script>
<div id="app">
  <custom-form @cancel="onCancel"></custom-form>
  <hr>
  <custom-form></custom-form>
</div>

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