What is the best way to extract value from an `observable<void>`?

Recently, I have been exploring Angular and encountered a situation where I need to retrieve a value from a method using subscription. The method in question is designed to return an object with properties {ClientId, ClientSecret}, but I must admit that I am still unclear on how exactly this method operates.

clientSecret(merchantId: number): Observable<void> {
    let url_ = this.baseUrl + "/api/PosQR/{merchantId}/client-secret";
    if (merchantId === undefined || merchantId === null)
        throw new Error("The parameter 'merchantId' must be defined.");
    url_ = url_.replace("{merchantId}", encodeURIComponent("" + merchantId));
    url_ = url_.replace(/[?&]$/, "");
    let options_ : any = {
        observe: "response",
        responseType: "blob",
        headers: new HttpHeaders({
        })
    };
    return this.http.request("get", url_, options_).pipe(_observableMergeMap((response_ : any) 
   => {
        return this.processClientSecret(response_);
    })).pipe(_observableCatch((response_: any) => {
        if (response_ instanceof HttpResponseBase) {
            try {
                return this.processClientSecret(response_ as any);
            } catch (e) {
                return _observableThrow(e) as any as Observable<void>;
            }
        } else
            return _observableThrow(response_) as any as Observable<void>;
    }));
}

In an attempt to subscribe to the method within ngOnInit and store the retrieved value in a local variable, I wrote:

this.posQrClient.clientSecret(2343).subscribe(res => {
    this.clientId = res[ClientId]
});

However, the output is returning null. Despite my attempts at troubleshooting, I have not been successful in resolving this issue. Any assistance or guidance would be greatly appreciated.

Answer №1

It appears that your subscription is in order, however, you are currently retrieving void values from the observable.

An Observable<void> provides a stream of void values. It seems like you actually need a stream of {ClientId, ClientSecret} values. To achieve this, adjust your function declaration to look like this:

clientSecret(merchantId: number): Observable<{clientSecret: string; clientId: string}> {...}

Ensure that you are returning the correct type as specified. If you prefer using any, you could also define it like so:

clientSecret(merchantId: number): Observable<any> {...}

However, I would not recommend this approach.

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