Vue component communication: using $emit to trigger child component events

Vue component communication: Use $emit to trigger sub-component events

In Vue development, component communication is a very important topic, because data transfer and interaction between components are the key to building complex applications . Vue provides a variety of ways to implement communication between components, one of which is to use $emit to trigger sub-component events. In this article, we will introduce how to use $emit for component communication in Vue and deepen the understanding through sample code.

First of all, we need to understand the basic usage of $emit. In Vue, each component can trigger a custom event through the $emit method. This event can be listened to in the parent component and respond accordingly. The $emit method accepts two parameters. The first parameter is the name of the event to be triggered, and the second parameter is the value to be passed to the event handling function. Here is an example:

// 子组件
Vue.component('child', {
  template: `
    <div>
      <button @click="triggerEvent()">点击触发事件</button>
    </div>
  `,
  methods: {
    triggerEvent() {
      this.$emit('custom-event', 'Hello World!');
    }
  }
});

// 父组件
Vue.component('parent', {
  template: `
    <div>
      <child @custom-event="handleEvent"></child>
    </div>
  `,
  methods: {
    handleEvent(value) {
      console.log(value); // 输出：Hello World!
    }
  }
});

// 应用程序
new Vue({
  el: '#app',
});

In the above code, the button click event in the child component will trigger a custom event named "custom-event" with "Hello World!" as a parameter Passed to the parent component. The event is listened to in the parent component and the received parameters are printed out in the event handler function.

Through this example, we can see that the child component triggers a custom event through the $emit method and passes the data to the parent component. This approach establishes a direct communication pipeline between parent and child components, making the data flow between components clearer and more controllable.

In addition to listening to the custom events of the child component through "@event name" in the parent component, we can also use the v-on directive to achieve the same effect. For example, the parent component can listen to the events of the child component like this:

<child v-on:custom-event="handleEvent"></child>

The effects achieved by these two methods are exactly the same, but the writing methods are slightly different.

In addition, $emit can also use modifiers to more precisely control the event delivery behavior. Commonly used modifiers are .stop, .prevent and .once. The .stop modifier is used to prevent the event from bubbling, the .prevent modifier is used to prevent the default event, and the .once modifier is used to trigger the event only once. The following is an example of using modifiers:

// 子组件
Vue.component('child', {
  template: `
    <div>
      <button @click.stop="triggerEvent()">点击触发事件</button>
    </div>
  `,
  methods: {
    triggerEvent() {
      this.$emit('custom-event', 'Hello World!');
    }
  }
});

In the above code, the .stop modifier prevents the event from bubbling, that is, the event will only be triggered in the child component and will not bubble to Parent component.

To summarize, using $emit to trigger subcomponent events is a common way to implement component communication in Vue. Through the $emit method, the child component can trigger a custom event and pass the data to the parent component, thus realizing data transfer and interaction between components. During development, we can use different modifiers according to needs to more precisely control the event delivery behavior. We hope that through the introduction and sample code of this article, readers can better understand and use the $emit method to implement communication between Vue components.

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