Vue3 $emit用法指南(含选项API、组合API及 setup 语法糖)

<template>
  <button @click="$emit('add', Math.random())">
    Add Math.random()
  </button>
</template>

<script setup>
import { ref } from 'vue'
const count = ref(0)
// 也可以从我们的模板中调用一个函数 `<ChildComponent @add="add" />
// const add = (i) => count.value += i
</script>
<template>
  <ChildComponent @add="(i) => count += i" /> 
  <p>Count: {{ count }}</p>
</template>

<script>
  export default {
      methods: {
          handleChange (event) {
              this.$emit("customChange", event.target.value.toUpperCase())
          }
      }
  }
</script>

<template>
  <div>
    <label>My Custom Input</label>
    <input type="text" placeholder="Custom input!" @input="handleChange" />
  </div>
</template>

<script>
  export default {
      methods: {
          handleChange (event) {
              this.$emit("customChange", event.target.value.toUpperCase())
          }
      }
  }
</script>

<template>
  <div>
    <label>My Custom Input</label>
    <input type="text" placeholder="Custom input!" @input="handleChange" />
  </div>
</template>

<script>
  export default {
    // can use the entire context object
    setup (props, context) {
        const handleChange = (event) => {
            context.emit("customChange", event.target.value)
        }
        return {
            handleChange
        }
    },
    // or we can destructure it and get `emit`
    setup (props, { emit }) { 
        const handleChange = (event) => {
            emit("customChange", event.target.value)
        }
        return {
            handleChange
        }
    }
  }
</script>

<template>
  <div>
    <label>My Custom Input</label>
    <input type="text" placeholder="Custom input!" @input="handleChange" />
  </div>
</template>

<script setup>
const emit = defineEmits(['customChange'])

const handleChange = (event) => {
  emit('customChange', event.target.value.toUpperCase())
}
</script>

<script setup>
const emit = defineEmits({
  unvalidatedEvent: null, // if we want an event without validation
  customChange: (s) => {
    if (s && typeof s === 'string') {
      return true
    } else {
      console.warn(`Invalid submit event payload!`)
      return false
    }
  },
})

const handleChange = (event) => {
  // no console warning
  emit('customChange', event.target.value.toUpperCase())
}

onMounted(() => {
  emit('customChange', 1) // not a string, warning!
})
</script>

<script>
  export default {
      emits: ["change"] // or can pass object with validators
  }
</script>
<template>
  <div>
    <label>My Custom Input</label>
    <input
      type="text"
      placeholder="Custom input!"
      @input='$emit("change", $event.target.value)'
    />
  </div>
</template>