What is method decorator in angular - amresh087/newronaRepos GitHub Wiki
In Angular, method decorators are used to modify the behavior of methods in a class. These decorators can be particularly useful for handling events, injecting dependencies, or adding custom functionality. Here are some common method decorators used in Angular
@HostListener(): This decorator is used to listen to events on the host element of a directive or component. It allows you to respond to user interactions or other events.
import { Directive, HostListener } from '@angular/core';
@Directive({
selector: '[appClickTracker]'
})
export class ClickTrackerDirective {
@HostListener('click', ['$event'])
onClick(event: Event) {
console.log('Element clicked:', event);
}
}
@HostBinding(): Although typically used as a property decorator, it can be used in conjunction with methods to dynamically bind properties to host element attributes.
import { Directive, HostBinding } from '@angular/core';
@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
private isHighlighted = false;
@HostBinding('class.highlighted') get highlighted() {
return this.isHighlighted;
}
toggleHighlight() {
this.isHighlighted = !this.isHighlighted;
}
}
@Inject(): This decorator is often used as a parameter decorator to inject dependencies, but can also be used with methods in advanced scenarios.
import { Injectable, Inject } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class MyService {
constructor(@Inject('SomeDependency') private dependency: any) {}
}
@Pipe(): While primarily used as a class decorator for defining pipes, method decorators can be used within pipes to define transformation logic.
import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
name: 'exponentialStrength'
})
export class ExponentialStrengthPipe implements PipeTransform {
@TransformMethod()
transform(value: number, exponent: string): number {
let exp = parseFloat(exponent);
return Math.pow(value, isNaN(exp) ? 1 : exp);
}
}
// Custom Method Decorator
function TransformMethod() {
return function(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
// Custom behavior here
};
}
While Angular itself doesn't provide many method decorators out-of-the-box beyond @HostListener, developers can create custom method decorators to add specific behavior or functionality to methods. Here is an example of creating a custom method decorator:
Custom method decorators can be used to add specific behavior or functionality to methods. Here's an example of how to create and use a custom method decorator:
// Custom Log decorator definition
function Log(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
const originalMethod = descriptor.value;
descriptor.value = function (...args: any[]) {
console.log(`Calling ${propertyKey} with arguments:`, args);
const result = originalMethod.apply(this, args);
console.log(`Result from ${propertyKey}:`, result);
return result;
};
return descriptor;
}
// Example service using the custom Log decorator
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class CalculationService {
@Log
multiply(a: number, b: number): number {
return a * b;
}
}
// Using the service
import { Component } from '@angular/core';
import { CalculationService } from './calculation.service';
@Component({
selector: 'app-root',
template: `<h1>Check the console for decorator logs</h1>`,
})
export class AppComponent {
constructor(private calculationService: CalculationService) {
this.calculationService.multiply(2, 3);
}
}