RxJS of() Example: Mocking Data with an Angular 7/8 Service and Observables

  • Author: Ahmed Bouchefra

RxJS' of() is a creational operator that allows you to create an RxJS Observable from a sequence of values.

According to the official docs:

of() converts the arguments to an observable sequence.

For example:

import { of } from 'rxjs';

of(1, 2, 3, 4)
.subscribe(
  next => console.log('next:', next),
  err => console.log('error:', err),
  () => console.log('Completed'),
);

This is a screenshot of the output:

RxJS of example

In Angular, you can use the of() operator to implement many use cases. For example, you can use it to mock data in your service for HttpClient.

Create an Angular 8 project, navigate to it and run the following command to generate a service:

$ ng generate service data

Next, open the src/app/data.service.ts file and start by importing the of() operator from rxjs:

import { Injectable } from '@angular/core';
import { of } from 'rxjs';


@Injectable({
  providedIn: 'root'
})
export class DataService {
}

Next, add a new products property to the service which contains the data we want to serve as our mocked response and a get() method that returns products as an RxJS Observable using the of() operator:

@Injectable({
  providedIn: 'root'
})
export class DataService {
  products: Array<object> = [
    { name: 'Product 001'},
    { name: 'Product 002'},
    { name: 'Product 003'},
    { name: 'Product 004'},
    { name: 'Product 005'}
  ];
  get() {
    return of(this.products);
  }
}

Next, let's subscribe to this observable in our component. Open the src/app/app.component.ts file, import the data service and susbscribe to the get() method as follows:

import { Component, OnInit } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-root',
  template: `<ul>
      <li *ngFor="let product of products">
        {{product.name}} 
      </li>
  </ul>`,
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit{
  title = 'Angular RxJS Examples';

  products: Array<object>;

  constructor(private dataService: DataService) { }

  ngOnInit() {
    this.dataService.get().subscribe(res => {
      this.products = res;
      console.log(res);
    });
  }
}

That's you should see your products displyed in an HTML list.

Conclusion

In this quick example, we have learned about the of() operator in RxJS and seen a real-world use case of it in the context of an Angular 8 app.


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