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Component v-model ​

Basic Usage ​

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

Starting in Vue 3.4, the recommended approach to achieve this is using the defineModel() macro:

vue
<!-- Child.vue -->
<script setup>
const model = defineModel()

function update() {
  model.value++
}
</script>

<template>
  <div>Parent bound v-model is: {{ model }}</div>
  <button @click="update">Increment</button>
</template>

The parent can then bind a value with v-model:

template
<!-- Parent.vue -->
<Child v-model="countModel" />

The value returned by defineModel() is a ref. It can be accessed and mutated like any other ref, except that it acts as a two-way binding between a parent value and a local one:

  • Its .value is synced with the value bound by the parent v-model;
  • When it is mutated by the child, it causes the parent bound value to be updated as well.

This means you can also bind this ref to a native input element with v-model, making it straightforward to wrap native input elements while providing the same v-model usage:

vue
<script setup>
const model = defineModel()
</script>

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

Try it in the playground

Under the Hood ​

defineModel is a convenience macro. The compiler expands it to the following:

  • A prop named modelValue, which the local ref's value is synced with;
  • An event named update:modelValue, which is emitted when the local ref's value is mutated.

This is how you would implement the same child component shown above prior to 3.4:

vue
<!-- Child.vue -->
<script setup>
const props = defineProps(['modelValue'])
const emit = defineEmits(['update:modelValue'])
</script>

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

Then, v-model="foo" in the parent component will be compiled to:

template
<!-- Parent.vue -->
<Child
  :modelValue="foo"
  @update:modelValue="$event => (foo = $event)"
/>

As you can see, it is quite a bit more verbose. However, it is helpful to understand what is happening under the hood.

Because defineModel declares a prop, you can therefore declare the underlying prop's options by passing it to defineModel:

js
// making the v-model required
const model = defineModel({ required: true })

// providing a default value
const model = defineModel({ default: 0 })

WARNING

If you have a default value for defineModel prop and you don't provide any value for this prop from the parent component, it can cause a de-synchronization between parent and child components. In the example below, the parent's myRef is undefined, but the child's model is 1:

js
// child component:
const model = defineModel({ default: 1 })

// parent component:
const myRef = ref()
html
<Child v-model="myRef"></Child>

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

template
<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:

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

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

template
<CustomInput
  :model-value="searchText"
  @update:model-value="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:

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

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

Now v-model should work perfectly with this component:

template
<CustomInput v-model="searchText" />

Try it in the Playground

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:

vue
<!-- 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>

v-model arguments ​

v-model on a component can also accept an argument:

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

In the child component, we can support the corresponding argument by passing a string to defineModel() as its first argument:

vue
<!-- MyComponent.vue -->
<script setup>
const title = defineModel('title')
</script>

<template>
  <input type="text" v-model="title" />
</template>

Try it in the Playground

If prop options are also needed, they should be passed after the model name:

js
const title = defineModel('title', { required: true })
Pre 3.4 Usage
vue
<!-- MyComponent.vue -->
<script setup>
defineProps({
  title: {
    required: true
  }
})
defineEmits(['update:title'])
</script>

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

Try it in the Playground

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

vue
<!-- 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>

Try it in the Playground

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:

template
<UserName
  v-model:first-name="first"
  v-model:last-name="last"
/>
vue
<script setup>
const firstName = defineModel('firstName')
const lastName = defineModel('lastName')
</script>

<template>
  <input type="text" v-model="firstName" />
  <input type="text" v-model="lastName" />
</template>

Try it in the Playground

Pre 3.4 Usage
vue
<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>

Try it in the Playground

vue
<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>

Try it in the Playground

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:

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

Modifiers added to a component v-model can be accessed in the child component by destructuring the defineModel() return value like this:

vue
<script setup>
const [model, modifiers] = defineModel()

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

<template>
  <input type="text" v-model="model" />
</template>

To conditionally adjust how the value should be read / written based on modifiers, we can pass get and set options to defineModel(). These two options receive the value on get / set of the model ref and should return a transformed value. This is how we can use the set option to implement the capitalize modifier:

vue
<script setup>
const [model, modifiers] = defineModel({
  set(value) {
    if (modifiers.capitalize) {
      return value.charAt(0).toUpperCase() + value.slice(1)
    }
    return value
  }
})
</script>

<template>
  <input type="text" v-model="model" />
</template>

Try it in the Playground

Pre 3.4 Usage
vue
<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="props.modelValue" @input="emitValue" />
</template>

Try it in the Playground

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:

vue
<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.

vue
<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>

Try it in the Playground

Modifiers for v-model with arguments ​

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

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

The corresponding declarations should be:

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

Here's another example of using modifiers with multiple v-model with different arguments:

template
<UserName
  v-model:first-name.capitalize="first"
  v-model:last-name.uppercase="last"
/>
vue
<script setup>
const [firstName, firstNameModifiers] = defineModel('firstName')
const [lastName, lastNameModifiers] = defineModel('lastName')

console.log(firstNameModifiers) // { capitalize: true }
console.log(lastNameModifiers) // { uppercase: true }
</script>
Pre 3.4 Usage
vue
<script setup>
const props = defineProps({
firstName: String,
lastName: String,
firstNameModifiers: { default: () => ({}) },
lastNameModifiers: { default: () => ({}) }
})
defineEmits(['update:firstName', 'update:lastName'])

console.log(props.firstNameModifiers) // { capitalize: true }
console.log(props.lastNameModifiers) // { uppercase: true }
</script>
vue
<script>
export default {
  props: {
    firstName: String,
    lastName: String,
    firstNameModifiers: {
      default: () => ({})
    },
    lastNameModifiers: {
      default: () => ({})
    }
  },
  emits: ['update:firstName', 'update:lastName'],
  created() {
    console.log(this.firstNameModifiers) // { capitalize: true }
    console.log(this.lastNameModifiers) // { uppercase: true }
  }
}
</script>

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