Vue.js

# v-model
кардинальное изменение

# 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;
  • BREAKING: v-bind's .sync modifier and component model option are removed and replaced with an argument on v-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" />
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# 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)
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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" />
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For convenience, we had a shorthand for this pattern with the .sync modifier:

<ChildComponent :title.sync="pageTitle" />
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# 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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v-bind anatomy

This also serves as a replacement to .sync modifier and allows us to have multiple v-models 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" />
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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 with v-model:

    <ChildComponent :title.sync="pageTitle" />

<!-- to be replaced with -->

<ChildComponent v-model:title="pageTitle" />
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  • for all v-models without arguments, make sure to change props and events name to modelValue and update:modelValue respectively

    <ChildComponent v-model="pageTitle" />
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    // 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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Migration build flags:

  • COMPONENT_V_MODEL
  • COMPILER_V_BIND_SYNC

# Next Steps

For more information on the new v-model syntax, see: