typescript - I need help understanding RxJx subscribe syntax -

this doing now, , wonder if there better way

this.dataservice.subscribe(     data => this.data = data,     error => alert('something went wrong'),     () => this.dosomethingoncompletion()); 

if i'm not catching data, however, might alter first of 3 functions:

() => null, 

the documentation rxjs 4.x doesn't answer question enough me. version 5.x explains less.

so, verdict? following wrong when need nothing more trigger happen?

this.dataservice.subscribe(     () => null,     error => alert('boom.'),     () => this.dosomethingoncompletion()); 

if didn't need on completion, i'd leave part out. if wanted check errors , nothing else?

rxjs 4 if need errors can use subscribeonerror method handles errors.

you can use subscribe method well, need pass null value handlers don't want, don't have pass own noop.

this.dataservice.subscribe(     null,     error => alert('something went wrong')); 

rxjs 5 can pass so-called partialobserver:

this.dataservice.subscribe({   error: error => alert('boom.'),    complete: () => this.dosomethingoncompletion() })