Master the art of utilizing Skip and Take functions in RxJs ObservableUncover the

Currently, I am in the process of learning about Angular 2, TypeScript, RxJs, and more. However, I have encountered an issue while attempting to return a subset of data within a service utilizing RxJs and Observables.

My expectation with the getCars function is that it will retrieve a JSON file, parse the data, and return only a portion of it based on specified offset and count parameters. Unfortunately, the problem lies in the fact that I am consistently receiving all of the data back (even though the file contains 200 entities/cars).

I am unsure of what mistake I might be making in this scenario.

EntityService

@Injectable()
export class EntityService {

  constructor(private http: Http) { }

  getCars(offset: number, count: number): Observable<Car[]> {
     return this.http
      .get('resources/data/cars.json')   
      .map(this.extractData)
      .skip(offset)
      .take(count)
      .catch(this.handleError);
  }

  private extractData(res: Response) {
    let body = res.json();
    return body.data || {};
  }

  private handleError(error: any) {
    // ...
  }
}

cars.json

    {
        "data":[
            {
                "vin":"ee8a89d8",
                "brand":"Fiat",
                "year":1987,
                "color":"Maroon"
            },
            {
                "vin":"642b3edc",
                "brand":"Renault",
                "year":1968,
                "color":"White"
            }
    ]
}

Answer №1

It's important to note that all data will be loaded through this method. The usage of the skip and take operators only comes into play when multiple events are present in the data flow:

  • skip: skip a certain number of events
  • take: consider only a specified number of events

For your specific scenario (an HTTP request), there is just one event: fetching the data. If you wish to filter the data, you'll need to incorporate a different map operator. Here's an example:

getCars(offset: number, count: number): Observable<Car[]> {
  return this.http
    .get('resources/data/cars.json')   
    .map(this.extractData)
    .map(data => {
      return data.slice(offset, offset + count); // <----
    })
    .catch(this.handleError);
}

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