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Angular lifecycle hooks

Angular lifecycle hooks

19 Jan 2024
Beginner
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5 min read

Angular lifecycle hooks: An Overview

One of the key features that make Angular versatile is its lifecycle hooks. These hooks enable developers to execute code at specific points in the component lifecycle, allowing for better control over the application's behavior.

In this article, we will delve into the world of Angular lifecycle hooks, exploring their types, purposes, and how they can be effectively leveraged in your applications. Additionally, we'll also delve into an Angular Certification Course and provide a comprehensive Angular Tutorial to help you enhance your skills.

What are Angular Component Lifecycle Hooks?

Angular components go through a series of lifecycle phases, starting from creation and ending with destruction. Each phase presents an opportunity for developers to execute custom logic, making it possible to respond to events and manage resources efficiently.

The component lifecycle consists of several hooks, and each hook corresponds to a specific phase in the lifecycle.

Types of Lifecycle Hooks

Angular provides eight lifecycle hooks, categorized into two groups: component lifecycle hooks and directive lifecycle hooks. Let's take a closer look at each type:

Component Lifecycle Hooks

  • ngOnChanges: Invoked when an input property binding changes.
  • ngOnInit: Called once, after the component is initialized.
  • ngDoCheck: Invoked during every change detection run, allowing custom change detection logic.
  • ngAfterContentInit: Triggered after content (projected content) has been initialized.
  • ngAfterContentChecked: Executed after every check of the content.

Directive Lifecycle Hooks

  • ngOnChanges: Similar to the component hook, it is triggered when the directive's input properties change.
  • ngOnInit: Analogous to the component hook, it is called once after the directive is initialized.
  • ngDoCheck: Similar to the component hook, it allows for custom change detection logic.
  • ngOnDestroy: Invoked just before the directive is destroyed.

How to Use Lifecycle Hooks

To leverage these hooks effectively, it's crucial to understand when each one is triggered and what actions are appropriate for each phase. Here's a brief guide on using some of the key hooks:

Lifecycle Hooks

1. ngOnChanges

Useful for responding to changes in input properties. It receives a SimpleChanges object that provides information about the changes.

ngOnChanges(changes: SimpleChanges) {
  // React to input property changes
}  

2. ngOnInit

Ideal for initializing component properties and fetching initial data. This hook is a good place to perform setup tasks that only need to occur once.

ngOnInit() {
  // Initialization logic here
} 

3. ngDoCheck

Implement custom change detection logic here. Be cautious with heavy computations, as this hook is called frequently.

ngDoCheck() {
  // Custom change detection logic
}

4. ngAfterContentInit

After the projected content (content projected into the component with <ng-content>) has been initialized, this hook is invoked.
ngAfterContentInit() { 
// After content intialization
}

5. ngAfterContentChecked

This hook is invoked at the end of each change detection cycle for the projected content.
ngAfterContentChecked() {
// content check
}

6. ngAfterViewInit

After the component's view (including its children) has been fully initialized, this hook is called.
ngAfterViewInit() { 
// view intialization
}

7. ngAfterViewChecked

This hook is invoked at the end of each change detection cycle for the component's view.
ngAfterViewChecked() {
  // Custom change detection logic
}

8. ngOnDestroy

Cleanup tasks, such as unsubscribing from observables and releasing resources, should be performed in this hook to avoid memory leaks.

ngOnDestroy() {
  // Cleanup logic here
}
Summary

Understanding Angular lifecycle hooks is essential for developing efficient and maintainable applications. By strategically using these hooks, developers can control the behavior of their components at different stages of the lifecycle.

Whether it's initializing data, responding to changes, or cleaning up resources, Angular lifecycle hooks provide a powerful mechanism for creating robust and responsive applications.

FAQs

Q1. How many life cycle hooks are there in Angular?

Angular gives us hooks so we can keep an eye on and react to events that happen throughout our component lifetime.

Q2. Which is the example of life cycle hooks?

All that angular hooks are are callback functions that are triggered when a certain event occurs within the component's life cycle. For example, when Angular first initializes a component, ngOnInit is called. Every time an Angular component's input property changes, ngOnChanges is called. 

Q3. What are lifecycle hooks and why are they important?

Use one or more of the Angular core library's lifecycle hook interfaces to handle events that arise during a component or directive's lifetime. You can act as Angular constructs, modifies, or destroys a component or directive instance through the hooks.

Q4. What is component lifecycle in Angular?

Angular itself controls a component's lifecycle. The Angular framework manages creation, rendering, and data-bound attributes. In addition, it offers hooks for reacting to important lifecycle events. 


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About Author
Shailendra Chauhan (Microsoft MVP, Founder & CEO at Scholarhat by DotNetTricks)

Shailendra Chauhan is the Founder and CEO at ScholarHat by DotNetTricks which is a brand when it comes to e-Learning. He provides training and consultation over an array of technologies like Cloud, .NET, Angular, React, Node, Microservices, Containers and Mobile Apps development. He has been awarded Microsoft MVP 8th time in a row (2016-2023). He has changed many lives with his writings and unique training programs. He has a number of most sought-after books to his name which has helped job aspirants in cracking tough interviews with ease.
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