VUE 3.4中的DexeModel宏是什么？

defineModel宏解决了Vue 3.4中自定义组件实现v-model时的冗余代码问题，1. 它在<script setup>中自动创建modelValue prop和update:modelValue事件，2. 支持通过参数自定义属性名和事件名，3. 可传递类型和默认值等选项，4. 作为编译时宏消除运行时开销，5. 使父子组件双向绑定更简洁高效，最终实现更少代码、相同行为、更清晰的意图。

The defineModel macro in Vue 3.4 is a compiler macro that simplifies two-way binding (v-model) in custom components by automatically creating a modelValue prop and an update:modelValue event — or a custom prop/event pair — with minimal boilerplate.

It was introduced in Vue 3.4 as a syntax sugar to make writing v-model-compatible components much cleaner, especially in <script setup></script>.

✅ What problem does it solve?

Before defineModel, if you wanted to support v-model in a component, you had to manually define:

<script setup>
defineProps(['modelValue'])
defineEmits(['update:modelValue'])
</script>

Then bind it in the template:

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

This is repetitive and verbose.

? How defineModel works

With defineModel, Vue automatically generates the prop and emit declaration:

<script setup>
const modelValue = defineModel()
</script>

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

This single line replaces both the prop and emit definition.

Under the hood, it’s equivalent to:

defineProps(['modelValue'])
defineEmits(['update:modelValue'])

But now you can directly read and write modelValue like a ref.

? Customizing the model

You can also use a custom prop name and event using arguments:

<script setup>
const checked = defineModel('checked', { type: Boolean })
</script>

<template>
  <input type="checkbox" v-model="checked">
</template>

This creates:

• A prop named checked
• An event named update:checked

You can even pass options like type, required, etc., just like with defineProps.

const count = defineModel('count', {
  type: Number,
  default: 0
})

⚠️ Important Notes

• defineModel is only available inside <script setup>.
• It’s a compiler macro, so it doesn’t exist at runtime. It gets compiled away during build.
• It only works in SFCs (Single File Components) with build tool support (e.g., Vite, Vue CLI).
• Not available in plain JavaScript or runtime-rendered components.

? Two-way binding made easy

Now parent usage stays the same:

<ChildComponent v-model="searchText" />

And the child handles it with zero boilerplate.

Summary

defineModel in Vue 3.4:

• Reduces boilerplate for v-model support
• Acts as a ref-like value that syncs with the parent
• Supports custom names and type options
• Is a compile-time helper (no runtime cost)

It’s a small but powerful quality-of-life improvement for component authors.

Basically: less code, same behavior, cleaner intent.

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