https://netbasal.com/inspiration-for-custom-decorators-in-angular-95aeb87f072c
以下代码使用了 class decorator, method decorator, property decorator
import { environment } from 'src/environments/environment'; import { Component, OnChanges, Input } from '@angular/core'; import { AppModule } from 'src/app/app.module'; import { Observable } from 'rxjs'; export function NgLog(): ClassDecorator { return (constructor: any) => { console.log('cons:', constructor); if (!environment.production) { // You can add/remove events for your needs const LIFECYCLE_HOOKS = [ 'ngOnInit', 'ngOnChanges', 'ngOnDestroy' ]; const component = constructor.name; LIFECYCLE_HOOKS.forEach(hook => { console.log('123:',hook); const original = constructor.prototype[hook]; constructor.prototype[hook] = function (...args) { console.log(`%c ${component} - ${hook}`, `color: #4CAF50; font-weight: bold`, ...args, constructor.prototype); original && original.apply(this, args); } }); } } } export function PageTrack(pageName: string): ClassDecorator { return function (constructor: any) { // const analyticsService = AppModule.injector.get(AnalyticsService); const ngOnInit = constructor.prototype.ngOnInit; constructor.prototype.ngOnInit = function (...args) { // analyticsService.visit(pageName); console.log(`%c visit: ${pageName}`, `color: #4CAF50; font-weight: bold`); ngOnInit && ngOnInit.apply(this, args); } const ngOnDestroy = constructor.prototype.ngOnDestroy; constructor.prototype.ngOnDestroy = function (...args) { // analyticsService.leave(pageName); console.log(`%c leave: ${pageName}`, `color: green; font-weight: bold`); ngOnDestroy && ngOnDestroy.apply(this, args); } } } export function log$(target: any, propertyKey: string) { let propertyValue; function getter() { return propertyValue; } function setter(value: any) { if (value instanceof Observable) { propertyValue = value.forEach(res => { const isArrayOfObjects = Array.isArray(res) && typeof res[0] === 'object'; const logType = isArrayOfObjects ? 'table' : 'log'; console.groupCollapsed(propertyKey); console[logType](res); console.groupEnd(); }); } else { console.error('none observable', value); propertyValue = value; } } Object.defineProperty(target, propertyKey, { get: getter, set: setter, enumerable: true, configurable: true }); } export function throttle(milliseconds: number = 500): MethodDecorator { return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) { const original = descriptor.value; descriptor.value = () => { console.error('throttle...........'); } return descriptor; }; } @Component({ selector: 'fly-aa', template: ` <div >zzzzz {{zz}}</div> ` }) @NgLog() @PageTrack("fly") export class FlyComponent implements OnChanges { @Input() @log$ zz: string; name = 'Angular'; mm() { console.log('m'); } @throttle() ngOnChanges(ss) { console.log('cha:', ss); } ngOnDestory(ss) { console.log('destroy:', ss); } }
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This post assumes that you at least have some working knowledge of Angular and Decorators.
If you have no prior knowledge on the subject, you can read the following articles:
- Make your Code Cleaner with Decorators
- Automagically Unsubscribe in Angular
- Decorators & metadata reflection in TypeScript: From Novice to Expert
NgLog Class Decorator
This decorator will be helpful for debugging purposes. We will log the ngOnInit
, ngOnDestroy
and ngOnChanges
lifecycle hooks.
import { environment } from "../environments/environment"; export function NgLog() : ClassDecorator { return function ( constructor : any ) { if( !environment.production ) { // You can add/remove events for your needs const LIFECYCLE_HOOKS = [ 'ngOnInit', 'ngOnChanges', 'ngOnDestroy' ]; const component = constructor.name; LIFECYCLE_HOOKS.forEach(hook => { const original = constructor.prototype[hook]; constructor.prototype[hook] = function ( ...args ) { console.log(`%c ${component} - ${hook}`, `color: #4CAF50; font-weight: bold`, ...args); original && original.apply(this, args); } }); } } }
We just log the hook and calling the original method. Let’s use the decorator.
@Component({ selector: 'posts-page', template: ` <posts [posts]="posts$ | async"></posts> ` }) @NgLog() export class PostsPageComponent { constructor( private store : Store<any> ) { this.posts$ = store.select('posts'); } } @Component({ selector: 'posts', template: ` <p *ngFor="let post of posts">{{post.title}}</p> ` }) @NgLog() export class PostsComponent implements OnInit { @Input() posts = []; }
Throttle Method Decorator
This decorator will be helpful when working for example with scroll events.
import t from 'lodash.throttle'; export function throttle( milliseconds : number = 500 ) : MethodDecorator { return function ( target : any, propertyKey : string, descriptor : PropertyDescriptor ) { const original = descriptor.value; descriptor.value = t(original, milliseconds); return descriptor; }; }
We are using the throttle
helper from lodash
and replacing the original method with our “throttle” version. Let’s use the decorator.
@Component({ selector: 'app-posts-page', template: ` <posts [posts]="posts$ | async"></posts> ` }) export class PostsPageComponent { constructor( private store : Store<any> ) { this.posts$ = store.select('posts'); } @HostListener('document:scroll') @throttle() scroll() { console.log('scroll'); } }
Track Page Class Decorator
This decorator will be helpful when you need to report page visits to your analytics provider.
import { AnalyticsService, AppModule } from "./app.module"; export function PageTrack( pageName : string ): ClassDecorator { return function ( constructor : any ) { const analyticsService = AppModule.injector.get(AnalyticsService); const ngOnInit = constructor.prototype.ngOnInit; constructor.prototype.ngOnInit = function ( ...args ) { analyticsService.visit(pageName); ngOnInit && ngOnInit.apply(this, args); } const ngOnDestroy = constructor.prototype.ngOnDestroy; constructor.prototype.ngOnDestroy = function ( ...args ) { analyticsService.leave(pageName); ngOnDestroy && ngOnDestroy.apply(this, args); } } }
Based on the hook we can call the appropriate method from our Analytics
service then invoke the original method.
@Component({ ... }) @PageTrack('blog') export class PostsPageComponent { constructor( private store : Store<any> ) { this.posts$ = store.select('posts').pluck('data'); } }
Log Observable Property Decorator
This decorator will be helpful for debugging purposes. You can also achieve the same thing with a custom operator.
export function log$( target : any, propertyKey : string ) { let propertyValue; function getter() { return propertyValue; } function setter( value : any ) { if( value instanceof Observable ) { propertyValue = value.do(res => { const isArrayOfObjects = Array.isArray(res) && typeof res[0] === 'object'; const logType = isArrayOfObjects ? 'table' : 'log'; console.groupCollapsed(propertyKey); console[logType](res) console.groupEnd(); }); } else { propertyValue = value; } } Object.defineProperty(target, propertyKey, { get: getter, set: setter, enumerable: true, configurable: true }); }
We can get the observable and add the do
operator to log the value. Based on the value we can choose between console.table
or console.log
.
Let’s use the decorator.
@Component({ selector: 'posts-page', template: ` <posts [posts]="posts$ | async"></posts> ` }) export class PostsPageComponent implements OnInit { @log$ posts$ : Observable<Post[]>; constructor( private store : Store<any> ) { this.posts$ = store.select('posts'); } }
Conclusion:
You can leverage decorators in your apps and create powerful things with them. Decorators are not only for frameworks or libraries, so be creative and start using them.
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