Angular
A guide to component lifecycle hooks in Angular
Need technical help?
Our experts will get back to you within 24 hours.
In developing dynamic and responsive web applications, Angular remains arguably the most powerful frame in existence today. Among other great features, Angular boasts a set of lifecycle hooks that enable a developer to intervene at various stages throughout the lifecycle of a component in an application. Actually, one must be familiar with these hooks while handling the initialization, update, and destruction of components.
In this blog post, I will explain Angular lifecycle hooks: What they are, how and when to use them, and best practices for implementation.
Every Angular component experiences a series of events from its birth till it is destroyed. This would include initialization, changes in the state or binding of data, and finally, clean-up. Angular allows this by providing developers with lifecycle hooks that make them sensitive to all key moments in the lifecycle of a component.
Lifecycle hooks are just the callback methods that Angular calls at certain times so you can have control over how your component behaves at each step.
Key Lifecycle Hooks
Let's discuss some of the most used Angular lifecycle hooks and their usages:
1. ngOnInit (Initialization)
The ngOnInit hook is called after all the data-bound properties of a directive/component have been initialized. You can easily guess that this is where you would place any initialization logic that you would want to run after your component has been initialized.
Usage:
Hook - when a component is being created, to fetch data from an API or service.
Initializing default values for a component property.
Example:
export class MyComponent implements OnInit { ngOnInit() { // Component initialization logic console.log("Component initialized"); }} 2. ngOnChanges (Reacting to input changes)
The ngOnChanges hook is invoked whenever an input property bound to the component changes. It helps a component react to changes in input values dynamically.
Usage:
- Whenever an @Input changes, update the component's state or logic.
Example:
export class MyComponent implements OnChanges { @Input() inputData: string; ngOnChanges(changes: SimpleChanges) { console.log("Input changed: ", changes.inputData); }}3. ngDoCheck (Custom Change Detection)
ngDoCheck is called on every change detection cycle. This lets you inject custom change detection logic into your app. This hook is more powerful but be careful: it is called extremely frequently.
Usage:
- When manually you need to detect and act on changes that Angular's default change detection doesn't catch.
Example:
export class MyComponent implements DoCheck { ngDoCheck() { console.log("Change detection running"); }}4. ngAfterContentInit (Content Projection Initialization)
This hook runs after Angular has rendered external content into your component (using <ng-content>). It is helpful when dynamically working with content projection.
Usage:
Handling everything relating to projection, such as accessing the projected elements.
export class MyComponent implements AfterContentInit { ngAfterContentInit() { console.log("Content projection initialized"); }}5. ngAfterContentChecked (Change Detection of Content Projection)
This hook is called after every change detection cycle that might have impacted the projected content. It's called when one wants to respond to the change in projected content.
Usage:
- If one wants to perform some action after Angular performs a change check on the content to be projected
Example:
export class MyComponent implements AfterContentChecked { ngAfterContentChecked() { console.log("Content projection checked for changes"); }}6. ngAfterViewInit(View Initialization)
This hook is called after the component's view, including all of its child views, has been initialized. This may be seen in cases where you need to perform operations that depend on the DOM being fully rendered like setting the focus for an input element.
Usage:
When you must access or change the DOM elements after the view has rendered.
Example:
export class MyComponent implements AfterViewInit { ngAfterViewInit() { console.log("View has been initialized"); }}7. ngAfterViewChecked (View Change Detection)
Similar to ngAfterContentChecked, this hook is called after every change detection cycle, but specifically for changes affecting the component's view and its child views.
Usage:
- When you need to perform actions or updates in response to view changes.
Example:
export class MyComponent implements AfterViewChecked { ngAfterViewChecked() { console.log("View checked for changes"); }}8. ngOnDestroy (Cleanup)
ngOnDestroy is invoked just before Angular compiles the component, therefore, it's the best location to set any cleanup requirements, such as deregistering observables or detaching event listeners in order to prevent memory leaks.
Usage:
- To run clean-up operations before component removal from the DOM.
Example:
export class MyComponent implements OnDestroy {
ngOnDestroy() { console.log("Component destroyed"); }}Why Lifecycle Hooks Matter
When you apply lifecycle hooks correctly, here are all the ways in which you are helped:
Performance Optimisation
You can ensure that resources are released on need. This is effortless as `ngOnDestroy` serves just that purpose.
Maintainability
You can hold and maintain the logic of initialization in `ngOnInit` and life-cycle related work in hooks, hence keeping your codebase cleaner and easier to comprehend.
Behavior
You respond to state changes dynamically, and your component behaves exactly as it should for the lifecycle stage.
Best Practices when using Lifecycle Hooks:
1. Do not over log your lifecycle hooks: Avoid putting too much logic in your lifecycle hooks. Delegate complex logic elsewhere in services or helper functions.
2. Minimize the use of ngDoCheck: Because this hook is called repeatedly, you don't want to call it too many times. Use it rarely and only when really required.
3. Unsubscribe from Observables: Unsubscribe all subscriptions in `ngOnDestroy` to avoid memory leaks.
Conclusion
Angular lifecycle hooks allow you to handle different phases of a component's life in a controlled way. You can make your Angular applications better, that is, predictable, maintainable, and efficient, with the help of these hooks. From initializing data to catching changes or cleanup, each lifecycle hook provides a well-defined purpose, allowing you to have fine-grained control over your components.
Knowing and conquering Angular lifecycle hooks is great for any developer working with Angular. It's helpful both in writing nicer code and in having your applications run smoothly and efficiently.
Ready to transform your business with our technology solutions? Contact Us today to Leverage Our Angular Expertise.
0
Angular
