Detailed explanation of the steps of value transfer function in Vue documentation

Vue.js is a popular JavaScript framework. One of its advantages is its powerful data binding capabilities. In Vue.js, data is passed through components, and in order to pass data between different components, Vue.js provides some value passing functions, such as $emit and $on. In this article, we will detail how to use these functions to implement value transfer.

1. Understand the basic concepts of component communication

When developing with Vue.js, you usually need to use multiple components to work together to build a complete application. Therefore, communication between components is very important, and they can help us implement various functions and interactions. In Vue.js, there are two ways to communicate between components:

• Communication between parent and child components
• Communication between sibling components

When communicating between parent and child components, you can use props and $emit functions. When communicating between sibling components, it can be achieved with the help of a common parent component.

2. Use $emit to implement communication between parent and child components

$emit() is a very important value transfer function in Vue.js, which is used for parent and child components communication between. The function of this function is to pass a custom event from the child component to the parent component and can pass some parameters.

The following are the steps to use $emit() to implement communication between parent and child components:

Step 1: Define a child component and use the $emit() function to trigger an event in the component.

<template>
  <div>
    <button @click="passData">传递数据</button>
  </div>
</template>

<script>
export default {
  methods: {
    passData() {
      this.$emit('get-data', 'Hello Vue')
    }
  }
}
</script>

In the above code, we define a subcomponent and define a button in it. When the button is clicked, the passData method is triggered, which uses the $emit() function to trigger a call called get -data event and carries a string parameter Hello Vue.

Step 2: Use the v-on directive in the parent component to listen to events triggered by the child component, and define a handler function to receive the parameters passed by the child component.

<template>
  <div>
    <child-component @get-data="getData"></child-component>
    <p>接收到子组件传递的数据：{{ data }}</p>
  </div>
</template>

<script>
import ChildComponent from './ChildComponent'
export default {
  components: { ChildComponent },
  data() {
    return {
      data: ''
    }
  },
  methods: {
    getData(data) {
      this.data = data
    }
  }
}
</script>

In the above code, we use the v-on instruction to listen to the event named get-data. When the subcomponent triggers the event, the method named getData will be called and the subcomponent will be The parameters passed are passed to the method. In this method, we assign the parameter to the data attribute to display the data passed by the child component in the parent component.

3. Use $on to implement communication between sibling components

$on() is another important value transfer function in Vue.js, which is used for sibling components communication between. The function of this function is to listen to a custom event in the child component and respond to the event.

The following are the steps to use $on() to implement communication between sibling components:

Step 1: Define a common parent component.

<template>
  <div>
    <child-component></child-component>
    <another-child-component></another-child-component>
  </div>
</template>

In the above code, we define a parent component that contains two child components.

Step 2: Use the $on() function in the child component to listen to a custom event.

<script>
export default {
  created() {
    this.$root.$on('trigger-event', this.handleEvent)
  },
  methods: {
    handleEvent() {
      console.log('Hello Vue!')
    }
  },
  destroyed() {
    this.$root.$off('trigger-event', this.handleEvent)
  }
}
</script>

In the above code, we use the created hook function to start listening to the event named trigger-event when the subcomponent is created. When the event is listened to, a method named handleEvent is called, which is used to handle the event. We also use the destroyed hook function to remove the event listener when the child component is destroyed to avoid memory leaks.

Step 3: Use the $emit() function in another child component to trigger the event.

<script>
export default {
  methods: {
    triggerEvent() {
      this.$root.$emit('trigger-event')
    }
  }
}
</script>

In the above code, we define a subcomponent and define a button in it. When the user clicks the button, the triggerEvent method is called, which triggers an event named trigger-event using the $emit() function.

4. Summary

In Vue.js, by using the $emit and $on functions, value transfer between parent-child components and sibling components can be achieved. First, we need to define the subcomponent and trigger a custom event using the $emit function inside it. Next, we need to use the v-on directive in the parent component to listen to the event and process the parameters passed by the child component in the handler function. For communication between sibling components, we need to use the $on function to listen to a custom event under a common parent component, and use the $emit function to trigger the event in another child component. These value transfer functions are a very important part of Vue.js. Mastering them allows us to better transfer data between components.

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