Obtaining a return value in TypeScript subscriptions

Question

Obtaining a return value in TypeScript subscriptions

How can I achieve success return from the Save() method?

public SaveItem() {
 if(save()){ // The intention is to use the save method like this
  // Close pop up;
}

public SaveAndNew() {
 if(save()){  // The intention is to use the save method like this
  // Create new item;
}


private save() {
 let issuccess = false;

 this.myservice.AddParty(newUserObject)
  .subscribe(data => {   
    if (data['status'].toString() === '1') {
      return issuccess = false;
    } else {
      return issuccess = true;
    }
  },
    (er) => {

      return issuccess = false;
    });
}

If I define save(): boolean, it will throw an error stating that Must return a value. If I return issuccess outside the subscribe block, it will always return a false value.

How can I await the save function and return a specific value based on the response?

I have researched callbacks and they do not seem elegant. Is there a more elegant way to accomplish this?

callbacks-vs-promises-vs-rxjs-vs-async-awaits

If this were C#, I would do the following:

var isSuccess = await SaveAsync(party);

angular typescript rxjs angular2-observables

Answer 1

Answer №1

If you modify your save method to return an observable with a boolean value, you can achieve the desired functionality.

public SaveAndCreateNew() {

this.save().subscribe(success =>
{
    if(success)
    {
      // Create new item here;
    }
});

private save() : Observable<boolean> {

 return this.myservice
            .AddParty(newUserObject)
            .map(data=> data['status'].toString() === '1')
            .catch(err => Observable.of(false)); 
}

Answer 2

If you modify your save method to return an observable with a boolean value, you can achieve the desired functionality.

public SaveAndCreateNew() {

this.save().subscribe(success =>
{
    if(success)
    {
      // Create new item here;
    }
});

private save() : Observable<boolean> {

 return this.myservice
            .AddParty(newUserObject)
            .map(data=> data['status'].toString() === '1')
            .catch(err => Observable.of(false)); 
}

Answer 3

Answer №2

How about implementing it in this way:

public SaveItem() {
 const isFresh = false;
 save(isFresh)
}

public SaveAndCreateNew() {
 const isFresh = true;
 save(isFresh)
}


private save(isFresh) {

 this.myservice.AddObject(newUserObject)
  .subscribe(data => {   
    if (data['status'].toString() === '1') {
      completeSave(isFresh);
    } else {
      failedSave(isFresh)
    }
  },
    (er) => {
      failedSave(isFresh)
    });
}

completeSave(isFresh) {
  // Handle case for new or existing item.
  // Close dialog box or perform necessary action
}

failedSave(isFresh) {
  // Implement specific actions in case of failure
}

Alternatively, TypeScript now provides support for async/await functionality which could be beneficial in this context. Refer to the following link for more details: https://medium.com/@benlesh/rxjs-observable-interop-with-promises-and-async-await-bebb05306875

Answer 4

How about implementing it in this way:

public SaveItem() {
 const isFresh = false;
 save(isFresh)
}

public SaveAndCreateNew() {
 const isFresh = true;
 save(isFresh)
}


private save(isFresh) {

 this.myservice.AddObject(newUserObject)
  .subscribe(data => {   
    if (data['status'].toString() === '1') {
      completeSave(isFresh);
    } else {
      failedSave(isFresh)
    }
  },
    (er) => {
      failedSave(isFresh)
    });
}

completeSave(isFresh) {
  // Handle case for new or existing item.
  // Close dialog box or perform necessary action
}

failedSave(isFresh) {
  // Implement specific actions in case of failure
}

Alternatively, TypeScript now provides support for async/await functionality which could be beneficial in this context. Refer to the following link for more details: https://medium.com/@benlesh/rxjs-observable-interop-with-promises-and-async-await-bebb05306875

Answer 5

Answer №3

If you find yourself in this situation, consider using the promise method instead of subscribe. When binding the data to HTML, it is recommended to utilize the async pipe.

Therefore, your service should be structured like this:

 AddParty(newUserObject) {
        return this.http.post(url)
            .toPromise().then(response => <any[]>response.json())
            .catch(error => {
                return error;
            });
    }

And when retrieving the data:

this.myservice.AddParty(newUserObject)
            .then(data => {
                if (data['status'].toString() === '1') {
                    return issuccess = false;
                } else {
                    return issuccess = true;
                }
            },
            (error) => {

                return issuccess = false;
            });
    }

Answer 6

If you find yourself in this situation, consider using the promise method instead of subscribe. When binding the data to HTML, it is recommended to utilize the async pipe.

Therefore, your service should be structured like this:

 AddParty(newUserObject) {
        return this.http.post(url)
            .toPromise().then(response => <any[]>response.json())
            .catch(error => {
                return error;
            });
    }

And when retrieving the data:

this.myservice.AddParty(newUserObject)
            .then(data => {
                if (data['status'].toString() === '1') {
                    return issuccess = false;
                } else {
                    return issuccess = true;
                }
            },
            (error) => {

                return issuccess = false;
            });
    }

Answer 7

Answer №4

Give this a shot:

function SaveItem() {
 if(performSave()){ 
  // Close the popup;
}

function SaveAndAddNew() {
 if(performSave()){  
  // Add new item;
}


async function performSave() {
 let isSuccess = false;

await myService.saveData(newUserData)
  .subscribe(response => {   
    if (response['status'].toString() === '1') {
      return isSuccess = false;
    } else {
      return isSuccess = true;
    }
  },
    (error) => {

      return isSuccess = false;
    });
      return isSuccess ;
}

Answer 8

Give this a shot:

function SaveItem() {
 if(performSave()){ 
  // Close the popup;
}

function SaveAndAddNew() {
 if(performSave()){  
  // Add new item;
}


async function performSave() {
 let isSuccess = false;

await myService.saveData(newUserData)
  .subscribe(response => {   
    if (response['status'].toString() === '1') {
      return isSuccess = false;
    } else {
      return isSuccess = true;
    }
  },
    (error) => {

      return isSuccess = false;
    });
      return isSuccess ;
}

Answer 9

Answer №5

In the subscribe() function, we have included an additional action parameter that allows for a return without using observables.

  public SaveItem() {
     if(save()){ // The save method is intended to be used like this
      // Close the popup;
    }

    public SaveAndNew() {
     if(save()){  // The save method is intended to be used like this
      // Create a new item;
    }


    private save() {
     let isSuccess = false;

     this.myservice.AddParty(newUserObject)
      .subscribe(data => {   
        if (data['status'].toString() === '1') {
          isSuccess = false;
        } else {
          isSuccess = true;
        }
      },
        (error) => {

          isSuccess = false;
        },
     () => {return isSuccess });
    }

Subscribe with 3 parameters

subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void):

Answer 10

In the subscribe() function, we have included an additional action parameter that allows for a return without using observables.

  public SaveItem() {
     if(save()){ // The save method is intended to be used like this
      // Close the popup;
    }

    public SaveAndNew() {
     if(save()){  // The save method is intended to be used like this
      // Create a new item;
    }


    private save() {
     let isSuccess = false;

     this.myservice.AddParty(newUserObject)
      .subscribe(data => {   
        if (data['status'].toString() === '1') {
          isSuccess = false;
        } else {
          isSuccess = true;
        }
      },
        (error) => {

          isSuccess = false;
        },
     () => {return isSuccess });
    }

Subscribe with 3 parameters

subscribe(next?: (value: T) => void, error?: (error: any) => void, complete?: () => void):

Obtaining a return value in TypeScript subscriptions

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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