https://netbasal.com/inspiration-for-custom-decorators-in-angular-95aeb87f072c

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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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【转】angular 自定义 component decorator

原文：https://www.cnblogs.com/oxspirt/p/14362644.html