What might be causing my observable to fail to return a value?

Question

What might be causing my observable to fail to return a value?

I'm currently utilizing an API known as ngx-pwa localstorage, which serves as a wrapper for an indexeddb database. Within my Angular project, I have a service that interacts with this database through a method called getItem:

getItem(key: string) {
    var data;
    this.storage.get(key).subscribe((dataPassed) => {
       console.log("data passed was", dataPassed);
       console.log("typeof ", typeof(dataPassed));
       console.log("data is?");
       data = dataPassed as string;
    });
    return data;
}

When calling this method within my Angular component, no data is returned despite finding the item in the subscribe method.

loadData(key) {
    console.log("storage from loaddb", this.storage.getItem(key)); // nothing is returned
}

Is there any way to successfully retrieve this data?

angular typescript

Answer 1

Answer №1

Asynchronous code operates in a way where you receive the result in a callback and cannot simply return it procedurally (unless you utilize async/await, but that is just a shortcut).

Instead of attempting to return a value directly, consider returning an observable and subscribing at the top layer.

getItem(key: string) {
return this.storage.get(key).pipe(tap((dataPassed) => {
//just peeking
   console.log("data passed was", dataPassed); 
   console.log("typeof ", typeof(dataPassed))
   console.log("data is?")
});
}

loadData(key) {
    console.log("storage from loaddb", 
this.storage.getItem(key)).subscribe((val){do stuff with value}) 
}

Note: There may be a missing colon or bracket somewhere.

Answer 2

Asynchronous code operates in a way where you receive the result in a callback and cannot simply return it procedurally (unless you utilize async/await, but that is just a shortcut).

Instead of attempting to return a value directly, consider returning an observable and subscribing at the top layer.

getItem(key: string) {
return this.storage.get(key).pipe(tap((dataPassed) => {
//just peeking
   console.log("data passed was", dataPassed); 
   console.log("typeof ", typeof(dataPassed))
   console.log("data is?")
});
}

loadData(key) {
    console.log("storage from loaddb", 
this.storage.getItem(key)).subscribe((val){do stuff with value}) 
}

Note: There may be a missing colon or bracket somewhere.

Answer 3

Answer №2

It's important to remember that returning data from an observable in the correct way is crucial. Make sure to return the observable from the service and then subscribe to it where you need the data. You can utilize various RxJS operators like tap for console logging side-effects, and map for data transformations.

Consider implementing the following code:

Service

getItem(key: string): Observable<any> {     // <-- make sure to return the observable
  return this.storage.get(key).pipe(
    tap((dataPassed) => {
      console.log("Data passed:", dataPassed); // Data is found but not returned
      console.log("Type of data:", typeof(dataPassed))
      console.log("Data is?")
    ),
    map(dataPassed => dataPassed as string)
  );
}

Component

data: string;

loadData(key) {
  console.log("Storage from loaddb", 
  this.storage.getItem(key).subscribe(
    datapassed => {
      this.data = datapassed;
      // Any further statements that depend on `this.data` should be inside the subscription
    }
  );
}

To learn more about asynchronous data handling and returning them correctly, check out this link.

Answer 4

It's important to remember that returning data from an observable in the correct way is crucial. Make sure to return the observable from the service and then subscribe to it where you need the data. You can utilize various RxJS operators like tap for console logging side-effects, and map for data transformations.

Consider implementing the following code:

Service

getItem(key: string): Observable<any> {     // <-- make sure to return the observable
  return this.storage.get(key).pipe(
    tap((dataPassed) => {
      console.log("Data passed:", dataPassed); // Data is found but not returned
      console.log("Type of data:", typeof(dataPassed))
      console.log("Data is?")
    ),
    map(dataPassed => dataPassed as string)
  );
}

Component

data: string;

loadData(key) {
  console.log("Storage from loaddb", 
  this.storage.getItem(key).subscribe(
    datapassed => {
      this.data = datapassed;
      // Any further statements that depend on `this.data` should be inside the subscription
    }
  );
}

To learn more about asynchronous data handling and returning them correctly, check out this link.

What might be causing my observable to fail to return a value?

Answer №1

Answer №2

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