The component instance cannot be accessed through this in the Vue 3 setup, but parent-child component communication can be achieved through expose and ref. 1. Use defineExpose to explicitly expose the method or responsive data of the child component. The parent component is called through ref; 2. The context information such as emit, attrs can be accessed through setupContext in the setup; 3. GetCurrentInstance can obtain complete component instances, but it is not officially recommended for business logic; 4. Common scenarios include manually triggering child component methods, controlling form verification, dynamic rendering of components, etc.
In setup() function of Vue 3, component instances will not be accessed by default through this like Vue 2. However, Vue provides mechanisms such as defineComponent and setupContext to help us obtain necessary context information, and even indirectly obtain component instances in some scenarios.
Expose child component methods or properties using expose
When you want to access certain methods or data of a child component from a parent component, you need to use expose to explicitly expose these in the child component. This is especially important in a combinatorial API, because by default, variables in the setup function are not automatically exposed to the parent component.
<script setup>
import { ref } from 'vue'
const count = ref(0)
function increment() {
count.value
}
//Expose method and responsive data defineExpose({ count, increment })
</script> Then get this child component instance through ref in the parent component:
<template>
<ChildComponent ref="childRef" />
</template>
<script setup>
import { ref, onMounted } from 'vue'
const childRef = ref()
onMounted(() => {
console.log(childRef.value.count) // You can access the exposed content childRef.value.increment()
})
</script>Get the current component instance in setup (not recommended)
Although Vue 3's Composition API design encourages you not to rely on component instances directly, if you do need to get the current component instance (such as in order to call the lifecycle hook or access $emit ), you can use setupContext .
export default {
setup(props, context) {
// context is an object containing attrs, slots, emit, etc. context.emit('someEvent') // equivalent to this.$emit
console.log(context.attrs) // Similar to this.$attrs
}
} Note: context here is not a complete component instance, but a part of its proxy. If you want to access the complete component instance, you can use getCurrentInstance() , but this is an official not recommended practice, mainly used in underlying scenarios such as plug-in development:
import { getCurrentInstance } from 'vue'
export default {
setup() {
const instance = getCurrentInstance()
console.log(instance) // Complete component instance (non-production environment only)
}
}?? Note:
proxyreturnedgetCurrentInstance()in the production environment isnull, so it cannot be used for business logic judgment.
Examples of practical application scenarios
Common usage scenarios include:
- Form components need to trigger verification manually (such as forms with Element Plus or Ant Design Vue)
- Manually control method calls to a subcomponent (such as refreshing, resetting)
- Dynamically render components and control their behavior through ref
For example, when using third-party UI libraries, it is often necessary to call methods inside the component through ref:
<template>
<MyTable ref="tableRef" />
</template>
<script setup>
import { ref } from 'vue'
const tableRef = ref()
async function refreshData() {
await tableRef.value.fetchData() // Call child component method}
</script> Basically that's it. The core is to understand the context mechanism in setup and how to realize communication and control between parent and child components through expose and ref .
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