Understanding Event Emission in Vue.js

Vue.js is a progressive JavaScript framework known for its simplicity and suitability for developing user interfaces. An important feature in Vue.js is the ability to handle communication between components which is mainly done using props and events. This article will discuss event emission from child to parent components using the this.$emit('eventName') method.

Emitting an Event from a Child Component to its parent Using “this.$emit('eventName')”

In Vue.js, the way to emit an event from a child component to its parent is to use the this.$emit('eventName') method. This method allows the child component to emit a custom event that the parent component can listen to. The eventName is a string that represents the name of the event. Detailed below is an example of how to emit an event:

// Child Component
methods: {
    buttonClicked: function () {
        this.$emit('buttonClicked');
    }
}

The parent component would listen for the buttonClicked event using a directive called v-on: or @ for short:

<!-- Parent Component -->
<child-component @buttonClicked="handleButtonClick"></child-component>

In the above examples, when a button is clicked in the child component (this is just an example, imagine that there's a button and when clicked it triggers the buttonClicked method), the 'buttonClicked' event is emitted. The parent component listens for the 'buttonClicked' event and runs a handleButtonClick method when it hears it.

It's important to note that Vue.js has a one-way data flow down the component hierarchy. Child components can't directly modify a value in the parent component. However, a child component can emit an event, and the parent component can listen for that event and respond to it, for example by changing its data.

In conclusion, when building applications with Vue.js, understanding how to use this.$emit('eventName') is important. It can facilitate how components communicate and share data with each other. Moreover, it accommodates the one-way data flow design of Vue.js, making application state easier to understand.