Re-throwing error from Observable.catch in AuthGuard canActivate

Question

I have the following code in AuthGuard's canActivate method:

 return this.http.get(url) .map(res => { console.log(res.json()); return true; }) .catch(error => { return Observable.throw(error); // return Observable.of(false); }); 

When I uncomment the Observable.of(false) line, all is well. However, I want to not only return false wrapped in an Observable, I also want to re-throw the error so that my global custom ErrorHandler would catch it and display a user-friendly message.

Answer 1

You can do this:

Observable.throw('error')
    .catch(error => {
        return Observable.throw(error).startWith(false);
    })
    .subscribe(
        value => console.log('Next', value),
        err => console.log('Error', err)
    );

The Observable returned from catch() is just a regular Observable that can throw errors as well.

Note that you have to set the error callback in subscribe() otherwise the error would be re-thrown.

This demo prints the following output:

Next: false
Error: error