What's the observable equivalent to `Promise.reject`

Question

I had this code

    return this.http.get(this.pushUrl)
        .toPromise()
        .then(response => response.json().data as PushResult[])
        .catch(this.handleError);

I wanted to use observable instead of Promise

how can i return the error to the calling method?

What's the equivalent to Promise.reject ?

    doSomeGet() {
        console.info("sending get request");

        this.http.get(this.pushUrl)
            .forEach(function (response) { console.info(response.json()); })
            .catch(this.handleError);
    }

    private handleError(error: any) {
        console.error('An error occurred', error);
        // return Promise.reject(error.message || error);
    }
}

the calling method was:

getHeroes() {
    this.pushService
        .doSomeGet();
        // .then(pushResult => this.pushResult = pushResult)
        // .catch(error => this.error = error);
}

The above code with ``Promise.reject`` uncommented works perfectly fine. I am not sure why. Do you have any thoughts on it? — raj, Nov 15 '16 at 22:39

Günter Zöchbauer · Accepted Answer · 2021-11-29T14:23:47.393

35

private handleError(error: any) {
    // previously 
    // return Observable.throw('Some error information');

    // now
    return throwError('Some error information');
}

See also How to catch exception correctly from http.request()?

edited Nov 29 '21 at 14:23

answered Aug 17 '16 at 10:22

Günter Zöchbauer

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this method seems to be deprecated in RXJS... prefer using the throwError operator: [here the documentation](https://www.learnrxjs.io/operators/creation/throw.html) – bertonc96 Mar 08 '19 at 11:39
1

this is deprecated. – Douglas Caina Nov 29 '21 at 14:17

MHX · Answer 2 · 2020-11-11T14:54:16.120

24

With RxJS 6 Observable.throw() has changed to throwError()

Observable.throw(new Error());

// becomes

throwError(new Error());

Source: RxJS v5.x to v6 Update Guide - Depracations

edited Nov 11 '20 at 14:54

answered Jul 11 '18 at 16:12

MHX

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score 0 · Answer 3 · answered Jan 20 '23 at 18:51

0

With RxJS 7 throwError(error: any) was marked obsolete due to be removed in v8

throwError(new Error());

// becomes

throwError(() => new Error());

Source: RxJS 6.x to 7.x

answered Jan 20 '23 at 18:51

Kent Bair

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1
1

What's the observable equivalent to `Promise.reject`

3 Answers3