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);
}
}
-------------------------------------------------------------
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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