Vue component communication: using $emit and $on for custom event communication

Vue component communication: Use $emit and $on for custom event communication

In Vue applications, component communication is a very important part. Through component communication, we can pass data, trigger events, etc. between different components. The Vue framework provides a variety of ways to communicate between components. One of the common ways is to use $emit and $on for custom event communication.

In Vue, each component can trigger a custom event through the $emit method and pass data to other components. Other components can listen to this custom event through $on and execute corresponding logic when the event is triggered.

Let's look at a simple example, assuming we have two components: one is the parent component Parent, and the other is the child component Child. We hope that when the button of the child component is clicked, the parent component will be notified to perform corresponding processing.

First, we need to define a button in the subcomponent and trigger a custom event when the button is clicked:

<template>
  <button @click="sendData">点击我触发事件</button>
</template>

<script>
export default {
  methods: {
    sendData() {
      this.$emit('customEvent', { data: 'hello' });
    }
  }
};
</script>

In the above code, the subcomponent defines a button and in In the click event of the button, a custom event named 'customEvent' is triggered through this.$emit, and an object containing data { data: 'hello' } is passed.

Then, in the parent component, we need to listen to this custom event and execute the corresponding logic when the event is triggered. We can use this.$on in the parent component's life cycle hook function created to listen to this custom event:

<template>
  <div>
    <p>{{ message }}</p>
    <child-component @customEvent="handleCustomEvent"></child-component>
  </div>
</template>

<script>
import ChildComponent from './ChildComponent.vue';

export default {
  components: {
    ChildComponent
  },
  data() {
    return {
      message: ''
    };
  },
  created() {
    this.$on('customEvent', this.handleCustomEvent);
  },
  methods: {
    handleCustomEvent(data) {
      this.message = data;
    }
  }
};
</script>

In the above code, the parent component first introduces the child component ChildComponent and uses it in the template tag to reference child components. Then, in the created life cycle hook function, listen to the 'customEvent' event triggered by the subcomponent through this.$on, and specify the callback function to be executed when the event is triggered as handleCustomEvent. In handleCustomEvent, we can get the data passed from the subcomponent and process it accordingly.

Now, we have completed the communication between the child component and the parent component. When the button of the child component is clicked, the 'customEvent' custom event is triggered and the data is passed to the parent component through this.$emit. After the parent component receives the data, it will be saved in the message variable and displayed in the template.

In addition to using this.$on to listen to custom events, we can also use this.$once to listen to custom events, so that after the event is triggered once, the monitoring will be automatically removed. In addition, Vue also provides this.$off method to manually remove the listener.

Summary:
Custom event communication through $emit and $on is a common component communication method in Vue. We can trigger a custom event and pass data through this.$emit in the sending component, and then listen to the custom event through this.$on in the receiving component and execute the corresponding logic when the event is triggered. This approach can help us achieve flexible communication between components and improve code reusability and maintainability.

The above is the sample code and instructions for using $emit and $on for custom event communication. I hope it can help you better understand and apply Vue component communication.

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