如何在地图中为主题观察者调用异常？

Question

I have this 0bserver subject:

public subject = new Subject<any>();

I push message like this:

this.subject.next({value : 1});

Then I try to do the following:

this.subject.map(data => {
      if (!data || !data.value) {
        throw new Error('No value, no function...');
      } else {
        return data;
      }
    }).subscribe((data: IFilterCustom) => {
      // WORK HERE WITH FILLED DATA
}, err => {
  console.error('Error');
});

I try to check if incoming data not contains value I invoke exception. How to do that?

Answer 1

In the latest rxjs you do this using pipes:

import { map, catchError } from 'rxjs/operators'
import { of } from 'rxjs'

this.subject.pipe(
  map((data) => {
    if (!data || !data.value) {
      throw new Error('No value, no function...');
    } else {
      return data;
    }
  }),
  catchError(() => {
    console.log('Error')
    return of(null) // Be sure to return an observable here! The 'of' function creates an observable out of the argument
  })
)

The catchError part will be called once an error has been thrown in the observable. This is also useful to catch any network errors in requests.

If you don't need error handing and you just need the subject not to emit values, then you can use filter

import { filter } from 'rxjs/operators'

this.subject.pipe(
  filter((data) => {
    return (data && data.value)
  })
)