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App.vue
CompOne.vue
main.js
 
<template>
  <h2>Example v-model Directive</h2>
  <p>App.vue 'text' property: "{{ text }}"</p>
  <comp-one v-model.allCapital="text"/>
</template>

<script>
export default {
  data() {
    return {
      text: ''
    }
  }
}
</script>                  
<template>
  <div>
    <h3>Component</h3>
    <p>Write something in the text input field below. Click somewhere else or use the tab key to shift focus away from the input element to see the effect of the custom 'allCapital' modifier.</p>
    <input 
      :value="modelValue" 
      @change="this.emitVal" 
    />
  </div>
</template>

<script>
export default {
  props: {
    modelValue: String,
    modelModifiers: {
      // modelModifiers is an empty object initially.
      // Modifiers set on the component will be stored here.
      default: () => ({}) 
    }
  },
  emits: ['update:modelValue'],
  methods: {
    emitVal(e) {
      let value = e.target.value
      if (this.modelModifiers.allCapital) {
        value = value.toUpperCase()
      }
      this.$emit('update:modelValue', value)
    }
  }
}
</script>

<style scoped>
div {
  border: solid black 1px;
  padding: 10px;
  margin: 20px 0;
  max-width: 500px;
}
</style>                  
import { createApp } from 'vue'

import App from './App.vue'
import CompOne from './components/CompOne.vue'

const app = createApp(App)
app.component('comp-one', CompOne)
app.mount('#app')
                  
http://localhost:5173/