通过angular2中http.get中的错误处理程序返回数据

Question

Trying to figure out something which probably has an obvious answer to someone not new to observables and angular2.

I am calling an http.get to fetch data from the server. However if there is some kind of error I want to return a predefined set of data. I realize that in my subscribe error function I can just load the pre-defined data there, but I want the service to take care of it.

So if I have a service doing this...

  getCategories(): Observable<string[]>  {

  return this.http.get('http://localhost:3000/categories/')
                .map(this.extractData)
                .catch(this.handleError);


}


private handleError (error: Response | any) {
  let errMsg: string = "some error message"
  //want to return a constant here return CATEGORIES;
  return Observable.throw(errMsg);
}

Instead of calling

return Observable.throw(errMsg);

How can I return data from the .catch function so that the subscriber wont know the difference - ie that its getting predefined data rather than data from the server.

My service call would look like this

this.myService.getCategories().subscribe(
                   cats => { this.categories = cats; },
                   error => {
                       console.log('Could not fetch categories', error)
                       //could do this but want it in service
                      //this.categories = CATEGORIES
                     },
                    () => console.log('Unknown error in get categories'));

Is there a different way to do this? Thanks

Answer 1

return this.http.get('http://localhost:3000/categories/')
           .map(this.extractData)
           .catch(() => Observable.of(CATEGORIES));

See the documentation