Angular Emit Event: A Comprehensive Guide to Child-to-Parent Component Communication

Introduction

Angular is a powerful web application framework for building modern, scalable, and maintainable applications. One of its core features is the ability to manage and pass data between components. In this blog post, we'll dive deep into the Angular event emitter, a mechanism for child-to-parent component communication, and demonstrate how to effectively implement this pattern in your Angular applications.

Overview of Angular Components and Communication

Components in Angular

Angular applications are composed of a hierarchy of components, which are reusable pieces of UI and logic that can be combined to build complex user interfaces. Each component is encapsulated, with its template, logic, and styles, making them highly modular and easy to maintain.

Component Communication In Angular,

There are several methods for components to communicate with each other, including input/output properties, services, and event emitters. In this blog, we'll focus on the event emitter method, which is ideal for child-to-parent component communication.

Angular EventEmitter: A Core Mechanism for Child-to-Parent Communication

The EventEmitter Class

Angular provides the EventEmitter class, which extends the RxJS Subject class, to facilitate communication between components. Event emitters allow child components to emit custom events that parent components can listen to and react to accordingly.

Creating an EventEmitter

To create an event emitter, import the EventEmitter class from the @angular/core module and instantiate it as a property of the child component, typically marked with the @Output() decorator.

Implementing the EventEmitter Pattern in Angular

Child Component

Emitting Events First, let's set up the child component to emit events. In the child component TypeScript file, import the EventEmitter and Output classes and create a new instance of the EventEmitter . In the child component's template, bind the event emitter to a DOM event, such as a button click.

Example:

code// child.component.ts 
import { Component, EventEmitter, Output } from '@angular/core'; 

@Component({ 
    selector: 'app-child', 
    template: ` <button (click)="onClick()">Click me</button> `, 
}) 

export class ChildComponent { 
    @Output() 
    buttonClicked = new EventEmitter<void>(); 
    
    onClick(): void { 
        this.buttonClicked.emit(); 
    } 
} 

Parent Component

Listening for Events Now, we'll set up the parent component to listen for the events emitted by the child component. In the parent component's template, bind a method to the custom event emitted by the child component.

Example:

code// parent.component.ts 
import { Component } from '@angular/core'; 

@Component({ 
    selector: 'app-parent', 
    template: ` <app-child (buttonClicked)="onChildButtonClick()"></app-child> `, 
}) 

export class ParentComponent { 
    onChildButtonClick(): void { 
        console.log('Button clicked in child component'); 
    } 
} 

Passing Data with EventEmitter

Emitting Data from the Child Component

The EventEmitter class can also emit data along with the event. To do this, simply provide a type parameter when instantiating the EventEmitter and pass the data to the emit() method.

Example:

code// child.component.ts 
@Output() 
buttonClicked = new EventEmitter<string>(); 

onClick(): void { 
    this.buttonClicked.emit('Hello, parent!'); 
} 

Receiving Data in the Parent Component

To receive the data emitted by the child component, update the parent component's event binding to pass the $event object to the event handler method.

Example:

code// parent.component.ts 
@Component({ 
    selector: 'app-parent', 
    template: ` <app-child (buttonClicked)="onChildButtonClick($event)"></app-child> `, 
}) 

export class ParentComponent { 
    onChildButtonClick(message: string): void { 
        console.log('Message from child component:', message); 
    } 
} 

EventEmitter Best Practices

Use the @Output() Decorator

Always use the @Output() decorator when creating event emitters in child components. This makes the code more readable and easier to understand by explicitly indicating that the property is meant to communicate with parent components.

Encapsulation and EventEmitter

Avoid directly manipulating the parent component's state from the child component. Instead, use the event emitter to pass data to the parent component and let the parent component handle any state changes or side effects.

Unsubscribe from EventEmitters

When using event emitters with custom observables, it's essential to unsubscribe from them when the component is destroyed to avoid memory leaks. You can do this by implementing the OnDestroy lifecycle hook and using the takeUntil() operator from RxJS.

Conclusion

Angular's event emitter is a powerful and flexible mechanism for child-to-parent component communication. By understanding how to implement the event emitter pattern, pass data between components, and adhere to best practices, you can create more maintainable and scalable Angular applications.