Ciclo de vida de componentes

What is the life cycle of a component in Angular?

Every component in Angular has a lifecycle, meaning that it goes through several events from the time it is created until it is destroyed. These events include its creation, update and eventual removal from the application. This understanding is crucial to manage component logic effectively and leverage Angular's capabilities for a seamless user experience.

How are lifecycle events developed?

The lifecycle of a component in Angular includes a specific set of events in order, such as constructor, ngOnChanges, ngOnInit, ngDoCheck, and finally ngOnDestroy. Here we break down these events:

1. Constructor: this is the first method that is executed when creating a component. Although it is a place to initialize variables, it is important to note that any asynchronous actions should not be placed at this point, as it is not recommended. It is especially useful for assigning values directly and prior to rendering the component.

2. ngOnChanges: Runs both before and during component rendering. It is useful to detect changes in the @Input and adapt the logic according to these variations.

3. ngOnInit: Runs only once after the changes have been applied and just before the component is rendered for the first time.

4. ngDoCheck: Provides an opportunity to detect and react to changes, to customize how the custom change detection works.

5. ngOnDestroy: Invoked just before Angular destroys the component. This is the perfect place to unsubscribe and free up resources.

Implementing the lifecycle in an Angular component.

To experiment with these events, let's create a simple component called Counter and an About page containing it. Let's follow along with some practical steps:

Creating the Counter component.

To work with the lifecycle, let's set up two inputs(@Input) inside the component:

 {import { Component, Input } from '@angular/core';
@Component({ selector: 'app-counter', template: '<p>Counter component loaded!</p>'})export class CounterComponent { @Input() duration: number = 0; @Input() message: string = '';
 constructor() { console.log('Constructor executed.'); }
 ngOnChanges(changes: SimpleChanges) { console.log('ngOnChanges executed.', changes); }
 ngOnInit() { console.log('ngOnInit executed.'); }
 ngDoCheck() { console.log('ngDoCheck executed.'); }
 ngOnDestroy() { console.log('ngOnDestroy executed.'); } } }}

Key aspects when creating a component

• Required Inputs: By default, duration is 0 and message is an empty string. TypeScript's inference engine helps to automatically detect their types.

• Constructor Usage: Only direct values should be defined. Avoid any actions involving promises or asynchronous processes.

• Change Tracking: Using ngOnChanges, you can identify which specifications have changed using the SimpleChanges object.

This knowledge of the lifecycle in Angular allows you to control when and how certain code segments are executed, optimizing the performance and logic of the component. With continued practice and debugging, they will become an essential tool in the development of complex applications. Go ahead and explore these concepts in your Angular projects!