The difference between $emit, $nextTick and $vnode in Vue

Vue is a popular front-end framework. The three concepts often used in daily development are $emit, $nextTick and $vnode. Although they look somewhat similar, they each have different functions and usage scenarios. Let’s learn about their differences one by one.

1. $emit

$emit is an instance method in Vue, used to communicate between parent components and child components. When a component needs to pass information to its parent component, it can trigger a custom event through the $emit method and carry some data information. The parent component can listen to the corresponding custom events and handle them accordingly.

For example:

Use the $emit method in the child component:

<button @click="$emit('add')">添加商品</button>

In the parent component, listen to the custom event and execute the corresponding method:

<template>
  <div>
    <my-component @add="addProduct"></my-component>
  </div>
</template>
<script>
export default {
  methods: {
    addProduct() {
      // TODO: 执行添加商品逻辑
    }
  }
}
</script>

2. $nextTick

$nextTick is an instance method in Vue, used to solve the timing problem of DOM operations and asynchronous data update. In Vue, template rendering is performed asynchronously. When the data is updated, Vue does not update the DOM elements immediately. Instead, the DOM update is postponed to the next tick. This process is called "asynchronous update queue".

Calling the $nextTick method after a data update ensures that the callback function is executed after the DOM update is completed. This mechanism is very useful. It can avoid a series of problems caused by directly operating DOM elements after DOM updates, and it can also better control the rendering timing of components.

For example:

<button @click="updateMsg">点击更新消息</button>

In the updateMsg method, you can use the $nextTick method to ensure that the callback function is executed after the DOM update is completed:

<script>
export default {
  data() {
    return {
      msg: 'Hello World!'
    }
  },
  methods: {
    updateMsg() {
      this.msg = 'Vue is awesome!'
      this.$nextTick(() => {
        console.log(this.$el.textContent) // 'Vue is awesome!'
      })
    }
  }
}
</script>

3. $vnode

$vnode is a special attribute in Vue, which represents the virtual node corresponding to the node currently being rendered. It is a read-only property and has a corresponding $vnode on each Vue component instance.

In the life cycle of Vue, the $vnode property will be updated each time the component is re-rendered, and can represent the status of the current component instance. In addition, the $vnode attribute can also be used to easily obtain information such as the parent-child relationship of the component and the name of the component.

For example:

<template>
  <div>
    <h1>{{ $vnode.componentOptions.Ctor.extendOptions.name }}</h1>
    <span>{{ $vnode.parent?.tag }}</span>
  </div>
</template>
<script>
export default {
  name: 'MyComponent'
}
</script>

In the above code, $vnode.componentOptions.Ctor.extendOptions.name can get the name of the current component, $vnode.parent?.tag can get the parent of the current component Level label name.

To sum up, although $emit, $nextTick and $vnode are very similar, they each have different functions and usage scenarios. $emit is used for communication between components, $nextTick is used to control the DOM update timing, and $vnode is used to obtain component information and status. In Vue development, making full use of these features can effectively improve the maintainability and performance of components.

The above is the detailed content of The difference between $emit, $nextTick and $vnode in Vue. For more information, please follow other related articles on the PHP Chinese website!