The data type 'Subscription' cannot be assigned

Question

The data type 'Subscription' cannot be assigned

Hello, I am having an issue with the code below that is making a rest call to a node.js backend endpoint in this ionic app. When I run the code, it gives me the following error. How can I resolve this?

Error:

ERROR in src/app/services/user.service.ts(22,5): error TS2322: Type 'Subscription' is not assignable to type 'Observable<any>'.
[ng]   Property '_isScalar' is missing in type 'Subscription'

TypeScript Code:

 //Method for user login
  loginService(username: string, password: string):Observable<any>
  { 
    return this.http.post(url+"/login",{"Username": username,"Password": password}).subscribe((val) => {console.log("POST call successful value returned in body",val);}, response => {  console.log("POST call in error", response); }, () => { console.log("The POST observable is now completed."); });
  }

angular typescript ionic-framework ionic4

Answer 1

Answer №1

It's quite clear from the error message that you have declared an observable but are returning a subscription instead. To rectify this, simply modify your code as follows:

loginService (Username: string, Password: string): Observable<any> { 
    return this.http.post(url + "/login", { Username, Password });
}

If you wish to add some postprocessing logic to your loginService, you can achieve this by using RxJS operators inside the pipe function. Here's an example:

return this.http.post(/* args */).pipe(
    tap(val => console.log('Success message. ', val),
    catchError(err => {
        console.error('Error message. ', err);
        return throwError(err);
    }))

Answer 2

It's quite clear from the error message that you have declared an observable but are returning a subscription instead. To rectify this, simply modify your code as follows:

loginService (Username: string, Password: string): Observable<any> { 
    return this.http.post(url + "/login", { Username, Password });
}

If you wish to add some postprocessing logic to your loginService, you can achieve this by using RxJS operators inside the pipe function. Here's an example:

return this.http.post(/* args */).pipe(
    tap(val => console.log('Success message. ', val),
    catchError(err => {
        console.error('Error message. ', err);
        return throwError(err);
    }))

Answer 3

Answer №2

this.http.post(url+"/login",{"Username": username,"Password": password})

is Observable<any>
However, the return type of Observable.subscribe is actually Subscription
Therefore, your function needs to be corrected like this:

loginService(username: string, password: string):Observable<any>
  { 
    return this.http.post(url+"/login",{"Username": username,"Password": password})
  }

class anotherClass {
    constructor(_loginService: loginService) {
        _loginService.subscribe((val) => {
            console.log("POST call successful value returned in body",val);
        }, response => {
            console.log("POST call in error", response); 
        }, () => {
            console.log("The POST observable is now completed.");
        });
    }
}

Answer 4

this.http.post(url+"/login",{"Username": username,"Password": password})

is Observable<any>
However, the return type of Observable.subscribe is actually Subscription
Therefore, your function needs to be corrected like this:

loginService(username: string, password: string):Observable<any>
  { 
    return this.http.post(url+"/login",{"Username": username,"Password": password})
  }

class anotherClass {
    constructor(_loginService: loginService) {
        _loginService.subscribe((val) => {
            console.log("POST call successful value returned in body",val);
        }, response => {
            console.log("POST call in error", response); 
        }, () => {
            console.log("The POST observable is now completed.");
        });
    }
}

Answer 5

Answer №3

http request will yield an Observable. Although you specified the return type as observable, in reality, you are subscribing to it within that method. Service functions should not perform subscriptions. Subscriptions should be handled from the component level.

//Function that executes user login
loginService(username: string, password: string):Observable<any>
{ 
  return this.http.post(url+"/login",{"Username": username,"Password": password});
}

Subscribe/ Access it from your component

this.yourService.loginService('test', 'test').subscribe(
    res => console.log(res), 
    err=> console.log(err)
);

Answer 6

http request will yield an Observable. Although you specified the return type as observable, in reality, you are subscribing to it within that method. Service functions should not perform subscriptions. Subscriptions should be handled from the component level.

//Function that executes user login
loginService(username: string, password: string):Observable<any>
{ 
  return this.http.post(url+"/login",{"Username": username,"Password": password});
}

Subscribe/ Access it from your component

this.yourService.loginService('test', 'test').subscribe(
    res => console.log(res), 
    err=> console.log(err)
);

The data type 'Subscription' cannot be assigned

Answer №1

Answer №2

Answer №3

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