Angular 6 return Observable

Question

I am new to Angular (used AngularJs for a number of years) and I am struggling with Observables :( I have this method:

filterProducts(categoryId: string, questions: Question[], organisationId: string): Observable<any> {
  var formulas = this.formulaService.getFromSelectedAnswers(questions);
  let shouldFilter = this.shouldFilterProducts(categoryId, questions, formulas);
  if (!shouldFilter) return;

  return this.filterOrScore(categoryId, organisationId, formulas).pipe(map(products => {
    if (!products || !products.length) return;

    this.products.length = 0;
    this.products.push.apply(this.products, products);
    this.questionService.filterQuestionsByProducts(products, questions);      
    this.questionService.updateSession(questions);
  }));
}

The line if (!shouldFilter) return; is not right. I need it to return an Observable so my subscriptions work. Does anyone know how to do that?

Possible duplicate of Return an empty Observable from an Angular2 Service — Martin Parenteau
– Martin Parenteau, Commented Oct 7, 2018 at 13:41

Suresh Kumar Ariya · Accepted Answer · 2018-10-07 13:38:06Z

2

You can return empty, if you don't care about return values in subscription. which will complete the observable.

import {empty} from 'rxjs';

filterProducts(categoryId: string, questions: Question[], organisationId: string): Observable<any> {
  var formulas = this.formulaService.getFromSelectedAnswers(questions);
  let shouldFilter = this.shouldFilterProducts(categoryId, questions, formulas);
  if (!shouldFilter) return empty();

  return this.filterOrScore(categoryId, organisationId, formulas).pipe(map(products => {
    if (!products || !products.length) return empty();

    this.products.length = 0;
    this.products.push.apply(this.products, products);
    this.questionService.filterQuestionsByProducts(products, questions);      
    this.questionService.updateSession(questions);
  }));

answered Oct 7, 2018 at 13:38

Suresh Kumar Ariya

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