v-model for child component and v-model inside chi

Question

Is there a way to simplify this code?

The button should also change the localValue of the child.

Vue.component('my-input', {
  template: `
    <div>
      <b>My Input:</b> <br>
      localValue: {{ localValue }} <br>
      <input v-model="localValue">
    </div>
  `,
  props: ['value'],
  data() {
    return { localValue: this.value }
  },
  watch: {
    value () {
      this.localValue = this.value
    },
    localValue () {
      this.$emit('input', this.localValue)
    }
  }
})

new Vue({
  el: '#app',
  data: () => ({
    parentValue: 'Inital value'
  }),
  methods: {
    change () {
      this.parentValue = 'Changed value'
    }
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.3/vue.min.js"></script>
<div id="app">
  <my-input v-model="parentValue"></my-input>

  <button @click="change">Change</button><br>

  parentValue: {{ parentValue }}
</div>

I have always faced difficulties when I need to do so.

I will be very grateful for the help!

Answer 1

If you avoid using v-model inside your custom form component, you really only need

<b>My Input:</b> <br>
localValue: {{ value }} <br>
<input :value="value" @input="$emit('input', $event.target.value)">

No data, no watch, that's it.

See https://vuejs.org/v2/guide/components.html#Using-v-model-on-Components

---

If you really want something representing a value local to your component, the Vue docs favour using computed values over watchers (ref: https://vuejs.org/v2/guide/computed.html#Watchers).

The idea here is to create a computed value with getter and setter to facilitate a simplified one-way data flow.

Vue.component('my-input', {
  template: `<div><b>My Input:</b> <br>localValue: {{ localValue }} <br><input v-model="localValue"></div>`,
  props: ['value'],
  computed: {
    localValue: {
      get () {
        return this.value
      },
      set (value) {
        this.$emit('input', value)
      }
    }
  }
})

new Vue({
  el: '#app',
  data: () => ({
    parentValue: 'Inital value'
  }),
  methods: {
    change () {
      this.parentValue = 'Changed value'
    }
  }
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.3/vue.min.js"></script>
<div id="app">
  <my-input v-model="parentValue"></my-input>

  <button @click="change">Change</button><br>

  parentValue: {{ parentValue }}
</div>