RxJs catch error and continue

Question

I have a list of items to parse, but the parsing of one of them can fail.

What is the "Rx-Way" to catch error but continue executing the sequence

Code Sample:

What I want to do in a non-Rx-Way:

var items = [0,1,2,3,4,5];

for (var item in items){
  try{
    if(item == 3){
      throw new Error("Value cannot be 3");
    }
    console.log(item);
  }catch(error){
     console.log("Error: " + error.message);
  }
}

Thanks in advance

Answer 1

I would suggest that you use flatMap (now mergeMap in rxjs version 5) instead, which will let you collapse errors if you don't care about them. Effectively, you will create an inner Observable that can be swallowed if an error occurs. The advantage of this approach is that you can chain together operators and if an error occurs anywhere in the pipeline it will automatically get forwarded to the catch block.

const {from, iif, throwError, of, EMPTY} = rxjs;
const {map, flatMap, catchError} = rxjs.operators;

// A helper method to let us create arbitrary operators
const {pipe} = rxjs;

// Create an operator that will catch and squash errors
// This returns a function of the shape of Observable<T> => Observable<R>
const mapAndContinueOnError = pipe(
  //This will get skipped if upstream throws an error
  map(v => v * 2),
  catchError(err => {
    console.log("Caught Error, continuing")
    //Return an empty Observable which gets collapsed in the output
    return EMPTY;
  })
)

const observable = from([0, 1, 2, 3, 4, 5]).pipe(
  flatMap((value) => 
    iif(() => value != 3, 
      of(value), 
      throwError(new Error("Value cannot be 3"))
    ).pipe(mapAndContinueOnError)
  )
);

observable.subscribe(
  (value) => console.log("onNext " + value), (error) => console.log("Error: " + error.message), () => console.log("Completed!")
);

<script src="https://unpkg.com/rxjs/bundles/rxjs.umd.min.js"></script>