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@ngrx/effects

RxJS powered side effect model for @ngrx/store

@ngrx/effects provides an API to model event sources as actions. Effects:

  • Listen for actions dispatched from @ngrx/store
  • Isolate side effects from components, allowing for more pure components that select state and dispatch actions
  • Provide new sources of actions to reduce state based on external interactions such as network requests, web socket messages and time-based events.

Installation

Install @ngrx/effects from npm:

npm install @ngrx/effects --save OR yarn add @ngrx/effects

Nightly builds

npm install github:ngrx/effects-builds OR yarn add github:ngrx/effects-builds

Setup

Effects are injectable service classes that use two main APIs.

Effect decorator

The @Effect() decorator provides metadata to register observable side-effects in the effects class. Registered effects provide new actions provided by the source Observable to the store.

Actions Observable

  • Represents an observable of all actions dispatched to the store.
  • Emits the latest action after the action has passed through all reducers.
  • The ofType operator lets you filter for actions of a certain type in which you want to use to perform a side effect.

Example

  1. Create an AuthEffects service that describes a source of login actions:
// ./effects/auth.effects.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Action } from '@ngrx/store';
import { Actions, Effect, ofType } from '@ngrx/effects';
import { Observable } from 'rxjs/Observable';
import { of } from 'rxjs/observable/of';
import { catchError, map, mergeMap } from 'rxjs/operators';

@Injectable()
export class AuthEffects {
  // Listen for the 'LOGIN' action
  @Effect() login$: Observable<Action> = this.actions$.pipe(
    ofType('LOGIN'),
    mergeMap(action =>
      this.http.post('/auth', action.payload).pipe(
        // If successful, dispatch success action with result
        map(data => ({ type: 'LOGIN_SUCCESS', payload: data })),
        // If request fails, dispatch failed action
        catchError(() => of({ type: 'LOGIN_FAILED' }))
      )
    )
  );
  

  constructor(
    private http: HttpClient,
    private actions$: Actions
  ) {}
}
  1. Register the EffectsModule in your application root imports. This NgModule must be added to your root NgModule for the effects providers to be registered and start when your application is loaded.
import { EffectsModule } from '@ngrx/effects';
import { AuthEffects } from './effects/auth.effects';

@NgModule({
  imports: [
    EffectsModule.forRoot([AuthEffects])
  ]
})
export class AppModule {}

Feature Modules

For feature modules, register your effects via EffectsModule.forFeature method in your module's imports:

import { EffectsModule } from '@ngrx/effects';
import { AdminEffects } from './effects/admin.effects';

@NgModule({
  imports: [
    EffectsModule.forFeature([AdminEffects])
  ]
})
export class AdminModule {}

API Documentation