v-model implementation in Vue.js 3

In Vue3, alias for v-model, e.g.:

<Comp v-model="vv">

is prop modelValue + event @update:modelValue :

<Comp :modelValue="vv" @update:modelValue="vv = $event">

So, to create v-model in vue, you just need to read from reactive modelValue property in the component and emit event named "@update:modelValue". Check example below to understand how to do it.

Example

Create file MyInp.vue :

<template>
  <div class="inpwrap">
    <div class="lbl" :class="modelValue || inpFoc ? 'fill' : ''">
      {{ label }}
    </div>
    <input 
      class="inp"
      :value="modelValue"
      @input="onInput"
      @focus='inpFoc = true'
      @blur='inpFoc = false'
    />
  </div>
</template>
<script>
export default {
  props: {
    modelValue: String,
    label: String,
  },
  data() {
    return {
      inpFoc: false,
    }
  },
  methods: {
    onInput(event) {
      this.$emit('update:modelValue', event.target.value)
    }
  },
}
</script>

<style scoped>
.inpwrap {
  width: 200px;
  margin-top: 30px;
  position: relative;
  margin-left: calc(50% - 100px);
}
.lbl {
  position: absolute;
  top: 10px;
  left: 10px;
  pointer-events: none;
  transition: 0.3s;
}
.lbl.fill {
  top: -8px;
  left: 5px;
  font-size: 14px;
  background-color: white;
  padding: 0 5px
}
.inp {
  width: 100%;
  box-sizing: border-box;
  padding: 10px;
  border: 1px solid #333;
  border-radius: 10px;
}
</style>

To connect file use:

<template>
  <div>
    <div>Hello, dear {{ name }} {{surname}}</div>
    <MyInp label="Name" v-model="name"></MyInp>
    <MyInp label="Surname" v-model="surname"></MyInp>
  </div>
</template>
<script>
import MyInp from './components/MyInp.vue'
export default {
  components: {
    MyInp
  },
  data() {
    return {
      name: '',
      surname: '',
    }
  },
}
</script>