Introduction to @Output and EventEmitter in Angular

Angular is a popular open-source front-end web application platform that allows developers to create dynamic and interactive web applications. One of the essential features of Angular is its component-based architecture, which enables developers to create reusable, independent components that can be used throughout the application.

When building applications with Angular components, it’s often necessary to communicate between them. This is where @Output and EventEmitter come into play – two essential tools that make it easy to pass data between components.

In this article, we’ll be taking a closer look at @Output and EventEmitter in Angular, discussing how they work, how to use them, and providing a few frequently asked questions.

What is @Output in Angular?

@Output is a decorator in Angular that allows a child component to communicate with a parent component. It enables the child component to emit an event and pass data back to the parent component. To use @Output, you need to create an EventEmitter instance inside the child component, decorate it with @Output, and emit an event whenever you want to pass data to the parent component.

What is EventEmitter in Angular?

EventEmitter is a class in the Angular core package that allows a component to emit an event. It’s commonly used with the @Output decorator to pass data from a child to a parent component. When creating an instance of EventEmitter, you have to specify a generic type to indicate the type of data the event will emit.

How to use @Output and EventEmitter in Angular?

To use @Output and EventEmitter in Angular, you need to follow these steps:

1. Create an EventEmitter instance inside the child component.
@Output() notifyParent: EventEmitter = new EventEmitter();
In this example, we’re creating an EventEmitter instance called notifyParent that will emit a string value.

2. Decorate the EventEmitter instance with the @Output decorator.
@Output() notifyParent: EventEmitter = new EventEmitter();
This makes the notifyParent instance available to the parent component.

3. Emit an event when you want to pass data to the parent component.
this.notifyParent.emit(‘Hello from child component!’);
Here, we are emitting an event when a button is clicked, passing the message ‘Hello from child component!’ to the parent component.

4. In the parent component, listen for the event emitted by the child component.

Here, we are listening for the notifyParent event and calling the onNotifyParent() function in the parent component.

5. Handle the emitted data in the parent component.
onNotifyParent(message: string) {
In this example, we’re simply logging the message to the console, but you could perform any action you wish with the emitted data.

Frequently Asked Questions about @Output and EventEmitter

Q: What’s the difference between @Input and @Output?
A: @Input allows a parent component to pass data to a child component, while @Output allows a child component to pass data back to the parent component.

Q: What’s the difference between EventEmitter and Subject?
A: EventEmitter is used to emit events in Angular, while Subject is a more powerful tool that allows you to observe and emit events in more complex scenarios.

Q: Can multiple components listen to the same event emitted by a child component?
A: Yes, you can listen to the same event emitted by a child component in multiple parent components.

Q: Can you pass multiple values with a single @Output?
A: Yes, you can pass multiple values with a single @Output by creating an object that contains all the values you want to pass and emitting that object.

Q: Can you use @Output to communicate between unrelated components?
A: No, @Output can only be used to communicate between a parent and a child component. For communication between unrelated components, you’ll need to use a service or other tools.

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