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Vue Tip: Event Handling

Vue Tip: Event Handling Image

In Vue, you can listen for events using the v-on directive or the shorthand @. You can listen for any DOM event; for example, you can use @click for click events. This link contains a list of all native DOM events.

Define Events

Of course, you can also listen for custom events that you have defined in your child component:

Child.vue
1<script setup lang="ts">
2import { ref } from 'vue'
3
4const counter = ref(0)
5
6const emit = defineEmits<{
7  (event: 'update:counter', counter: number): void
8}>()
9
10const increment = () => {
11  counter.value++
12  emit('update:counter', counter.value)
13}
14</script>
15
16<template>
17  <div>
18    <span>Counter: {{ counter }}</span>
19    <button @click="increment">Increment</button>
20  </div>
21</template>

Handle Events

Let's look at the different ways to handle such events in Vue.

Without arguments

If your event does not have any arguments, I prefer this syntax:

Parent.vue
1<script setup lang="ts">
2import Child from './Child.vue'
3
4const onUpdateCounter = (counter: number) => {
5  console.log('onUpdateCounter', counter)
6}
7</script>
8
9<template>
10  <Child @update:counter="onUpdateCounter" />
11</template>

Access custom event object

If you want to access the custom event object in your event handler, you can use the following syntax:

Parent.vue
1<script lang="ts" setup>
2import type { Counter } from '...'
3
4const counters: Counter[] = [
5  // ...
6]
7
8function onUpdateCounter(counter: Counter) {
9  // ...
10}
11</script>
12
13<template>
14  <ul>
15    <li v-for="counter of counter" :key="counter.id">
16      <Child @update:counter="() => onUpdateCounter(counter)" />
17    </li>
18  </ul>
19</template>

Access custom & native event object

Sometimes, you need access to your custom event object and the native event object. In this case, you can use the following syntax:

Parent.vue
1<script lang="ts" setup>
2import type { Counter } from '...'
3
4const counters: Counter[] = [
5  // ...
6]
7
8function onUpdateCounter(event: Event, counter: Counter) {
9  // ...
10}
11</script>
12
13<template>
14  <ul>
15    <li v-for="counter of counter" :key="counter.id">
16      <Child @update:counter="($event) => onUpdateCounter($event, counter)" />
17    </li>
18  </ul>
19</template>

Further Reading

Lachlan Miller wrote an excellent in-depth article about event handling, which you can find here. It is definitely worth a read!