Component v-model #

v-model can be used on a component to implement a two-way binding.

First let's revisit how v-model is used on a native element:

<input v-model="searchText" />

Under the hood, the template compiler expands v-model to the more verbose equivalent for us. So the above code does the same as the following:

<input
  :value="searchText"
  @input="searchText = $event.target.value"
/>

When used on a component, v-model instead expands to this:

<CustomInput
  :modelValue="searchText"
  @update:modelValue="newValue => searchText = newValue"
/>

For this to actually work though, the <CustomInput> component must do two things:

1. Bind the value attribute of a native <input> element to the modelValue prop
2. When a native input event is triggered, emit an update:modelValue custom event with the new value

Here's that in action:

<!-- CustomInput.vue -->
<script>
export default {
  props: ['modelValue'],
  emits: ['update:modelValue']
}
</script>

<template>
  <input
    :value="modelValue"
    @input="$emit('update:modelValue', $event.target.value)"
  />
</template>

<!-- CustomInput.vue -->
<script setup>
defineProps(['modelValue'])
defineEmits(['update:modelValue'])
</script>

<template>
  <input
    :value="modelValue"
    @input="$emit('update:modelValue', $event.target.value)"
  />
</template>

Now v-model should work perfectly with this component:

<CustomInput v-model="searchText" />

Another way of implementing v-model within this component is to use a writable computed property with both a getter and a setter. The get method should return the modelValue property and the set method should emit the corresponding event:

<!-- CustomInput.vue -->
<script>
export default {
  props: ['modelValue'],
  emits: ['update:modelValue'],
  computed: {
    value: {
      get() {
        return this.modelValue
      },
      set(value) {
        this.$emit('update:modelValue', value)
      }
    }
  }
}
</script>

<template>
  <input v-model="value" />
</template>

<!-- CustomInput.vue -->
<script setup>
import { computed } from 'vue'

const props = defineProps(['modelValue'])
const emit = defineEmits(['update:modelValue'])

const value = computed({
  get() {
    return props.modelValue
  },
  set(value) {
    emit('update:modelValue', value)
  }
})
</script>

<template>
  <input v-model="value" />
</template>

v-model arguments #

By default, v-model on a component uses modelValue as the prop and update:modelValue as the event. We can modify these names passing an argument to v-model:

<MyComponent v-model:title="bookTitle" />

In this case, the child component should expect a title prop and emit an update:title event to update the parent value:

<!-- MyComponent.vue -->
<script setup>
defineProps(['title'])
defineEmits(['update:title'])
</script>

<template>
  <input
    type="text"
    :value="title"
    @input="$emit('update:title', $event.target.value)"
  />
</template>

<!-- MyComponent.vue -->
<script>
export default {
  props: ['title'],
  emits: ['update:title']
}
</script>

<template>
  <input
    type="text"
    :value="title"
    @input="$emit('update:title', $event.target.value)"
  />
</template>

Multiple v-model bindings #

By leveraging the ability to target a particular prop and event as we learned before with v-model arguments, we can now create multiple v-model bindings on a single component instance.

Each v-model will sync to a different prop, without the need for extra options in the component:

<UserName
  v-model:first-name="first"
  v-model:last-name="last"
/>

<script setup>
defineProps({
  firstName: String,
  lastName: String
})

defineEmits(['update:firstName', 'update:lastName'])
</script>

<template>
  <input
    type="text"
    :value="firstName"
    @input="$emit('update:firstName', $event.target.value)"
  />
  <input
    type="text"
    :value="lastName"
    @input="$emit('update:lastName', $event.target.value)"
  />
</template>

<script>
export default {
  props: {
    firstName: String,
    lastName: String
  },
  emits: ['update:firstName', 'update:lastName']
}
</script>

<template>
  <input
    type="text"
    :value="firstName"
    @input="$emit('update:firstName', $event.target.value)"
  />
  <input
    type="text"
    :value="lastName"
    @input="$emit('update:lastName', $event.target.value)"
  />
</template>

Handling v-model modifiers #

When we were learning about form input bindings, we saw that v-model has built-in modifiers - .trim, .number and .lazy. In some cases, you might also want the v-model on your custom input component to support custom modifiers.

Let's create an example custom modifier, capitalize, that capitalizes the first letter of the string provided by the v-model binding:

<MyComponent v-model.capitalize="myText" />

Modifiers added to a component v-model will be provided to the component via the modelModifiers prop. In the below example, we have created a component that contains a modelModifiers prop that defaults to an empty object:

<script setup>
const props = defineProps({
  modelValue: String,
  modelModifiers: { default: () => ({}) }
})

defineEmits(['update:modelValue'])

console.log(props.modelModifiers) // { capitalize: true }
</script>

<template>
  <input
    type="text"
    :value="modelValue"
    @input="$emit('update:modelValue', $event.target.value)"
  />
</template>

<script>
export default {
  props: {
    modelValue: String,
    modelModifiers: {
      default: () => ({})
    }
  },
  emits: ['update:modelValue'],
  created() {
    console.log(this.modelModifiers) // { capitalize: true }
  }
}
</script>

<template>
  <input
    type="text"
    :value="modelValue"
    @input="$emit('update:modelValue', $event.target.value)"
  />
</template>

Notice the component's modelModifiers prop contains capitalize and its value is true - due to it being set on the v-model binding v-model.capitalize="myText".

Now that we have our prop set up, we can check the modelModifiers object keys and write a handler to change the emitted value. In the code below we will capitalize the string whenever the <input /> element fires an input event.

<script setup>
const props = defineProps({
  modelValue: String,
  modelModifiers: { default: () => ({}) }
})

const emit = defineEmits(['update:modelValue'])

function emitValue(e) {
  let value = e.target.value
  if (props.modelModifiers.capitalize) {
    value = value.charAt(0).toUpperCase() + value.slice(1)
  }
  emit('update:modelValue', value)
}
</script>

<template>
  <input type="text" :value="modelValue" @input="emitValue" />
</template>

<script>
export default {
  props: {
    modelValue: String,
    modelModifiers: {
      default: () => ({})
    }
  },
  emits: ['update:modelValue'],
  methods: {
    emitValue(e) {
      let value = e.target.value
      if (this.modelModifiers.capitalize) {
        value = value.charAt(0).toUpperCase() + value.slice(1)
      }
      this.$emit('update:modelValue', value)
    }
  }
}
</script>

<template>
  <input type="text" :value="modelValue" @input="emitValue" />
</template>

For v-model bindings with both argument and modifiers, the generated prop name will be arg + "Modifiers". For example:

<MyComponent v-model:title.capitalize="myText">

The corresponding declarations should be:

const props = defineProps(['title', 'titleModifiers'])
defineEmits(['update:title'])

console.log(props.titleModifiers) // { capitalize: true }

export default {
  props: ['title', 'titleModifiers'],
  emits: ['update:title'],
  created() {
    console.log(this.titleModifiers) // { capitalize: true }
  }
}