# v-model
breaking
# Overview
In terms of what has changed, at a high level:
- BREAKING: When used on custom components,
v-model
prop and event default names are changed:- prop:
value
->modelValue
; - event:
input
->update:modelValue
;
- prop:
- BREAKING:
v-bind
's.sync
modifier and componentmodel
option are removed and replaced with an argument onv-model
; - NEW: Multiple
v-model
bindings on the same component are possible now; - NEW: Added the ability to create custom
v-model
modifiers.
For more information, read on!
# Introduction
When Vue 2.0 was released, the v-model
directive required developers to always use the value
prop. And if developers required different props for different purposes, they would have to resort to using v-bind.sync
. In addition, this hard-coded relationship between v-model
and value
led to issues with how native elements and custom elements were handled.
In 2.2 we introduced the model
component option that allows the component to customize the prop and event to use for v-model
. However, this still only allowed a single v-model
to be used on the component.
With Vue 3, the API for two-way data binding is being standardized in order to reduce confusion and to allow developers more flexibility with the v-model
directive.
# 2.x Syntax
In 2.x, using a v-model
on a component was an equivalent of passing a value
prop and emitting an input
event:
<ChildComponent v-model="pageTitle" />
<!-- would be shorthand for: -->
<ChildComponent :value="pageTitle" @input="pageTitle = $event" />
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If we wanted to change prop or event names to something different, we would need to add a model
option to ChildComponent
component:
<!-- ParentComponent.vue -->
<ChildComponent v-model="pageTitle" />
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// ChildComponent.vue
export default {
model: {
prop: 'title',
event: 'change'
},
props: {
// this allows using the `value` prop for a different purpose
value: String,
// use `title` as the prop which take the place of `value`
title: {
type: String,
default: 'Default title'
}
}
}
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So, v-model
in this case would be a shorthand to
<ChildComponent :title="pageTitle" @change="pageTitle = $event" />
# Using v-bind.sync
In some cases, we might need "two-way binding" for a prop (sometimes in addition to existing v-model
for the different prop). To do so, we recommended emitting events in the pattern of update:myPropName
. For example, for ChildComponent
from the previous example with the title
prop, we could communicate the intent of assigning a new value with:
this.$emit('update:title', newValue)
Then the parent could listen to that event and update a local data property, if it wants to. For example:
<ChildComponent :title="pageTitle" @update:title="pageTitle = $event" />
For convenience, we had a shorthand for this pattern with the .sync
modifier:
<ChildComponent :title.sync="pageTitle" />
# 3.x Syntax
In 3.x v-model
on the custom component is an equivalent of passing a modelValue
prop and emitting an update:modelValue
event:
<ChildComponent v-model="pageTitle" />
<!-- would be shorthand for: -->
<ChildComponent
:modelValue="pageTitle"
@update:modelValue="pageTitle = $event"
/>
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# v-model
arguments
To change a model name, instead of a model
component option, now we can pass an argument to v-model
:
<ChildComponent v-model:title="pageTitle" />
<!-- would be shorthand for: -->
<ChildComponent :title="pageTitle" @update:title="pageTitle = $event" />
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This also serves as a replacement to .sync
modifier and allows us to have multiple v-model
s on the custom component.
<ChildComponent v-model:title="pageTitle" v-model:content="pageContent" />
<!-- would be shorthand for: -->
<ChildComponent
:title="pageTitle"
@update:title="pageTitle = $event"
:content="pageContent"
@update:content="pageContent = $event"
/>
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# v-model
modifiers
In addition to 2.x hard-coded v-model
modifiers like .trim
, now 3.x supports custom modifiers:
<ChildComponent v-model.capitalize="pageTitle" />
Read more about custom v-model
modifiers in the Custom Events section.
# Migration Strategy
We recommend:
checking your codebase for
.sync
usage and replace it withv-model
:<ChildComponent :title.sync="pageTitle" /> <!-- to be replaced with --> <ChildComponent v-model:title="pageTitle" />
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v-model
s without arguments, make sure to change props and events name tomodelValue
andupdate:modelValue
respectively<ChildComponent v-model="pageTitle" />
1// ChildComponent.vue export default { props: { modelValue: String // previously was `value: String` }, emits: ['update:modelValue'], methods: { changePageTitle(title) { this.$emit('update:modelValue', title) // previously was `this.$emit('input', title)` } } }
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COMPONENT_V_MODEL
COMPILER_V_BIND_SYNC
# Next Steps
For more information on the new v-model
syntax, see: