How do I return a different Promise only if first Promise errors out?

The specific situation is:

Maybe I'm just not understanding Promises well enough.

Here's non-working code of what I want to do, but I don't know how the syntax works.

getUserProfile()
return this.storage.get("userProfile")
.then(user =>
if (user == null)
throw new Error("no user profile");


)
.catch(error =>
//I don't know how to return a different promise
return this.getUserProfileWithHttpCall();

);


//I want to return this in getUserProfile() if "userProfile" doesn't exist in "storage"
getUserProfileWithHttpCall(): Promise < UserProfile >
return this.http.get(this.baseUrl + "/Account/GetUserInfo")
.toPromise()
.then(
response =>
this.storage.set("userProfile", response);
return response;

);



this.storage is Storage from "@ionic/storage"

this.storage

this.http is HttpClient '@angular/common/http'

this.http

1 Answer
1

For your idea, there is no need to throw any error. You can do this:

getUserProfile() this.getUserProfileWithHttpCall()
);



Or in the await, async way:

await

async

async getUserProfile()
return (await this.storage.get("userProfile"))


Maybe you want to rather use Observables, because they are the hip thing these days. you can change it to this:

Observables

getUserProfile()
return from(this.storage.get("userProfile")).pipe(
concatMap((user) => user ? of(user) : this.getUserProfileWithHttpCall())
);



You have to change your getUserProfileWithHttpCall then:

getUserProfileWithHttpCall(): Observable<UserProfile>
return this.http.get(`$this.baseUrl/Account/GetUserInfo`).pipe(
tap((user:UserProfile) => this.storage.set("userProfile", user))
)



Much neater :)

And finally, to explain why your method is not working, is because you are not returning the user in the then when it's not null, if you don't want to change your code so 'drastically', you can also just do this:

then

getUserProfile()
return this.storage.get("userProfile")
.then(user =>
if (user == null)
throw new Error("no user profile");


return user; // you missed this one

)
.catch(error =>
//I don't know how to return a different promise
// Like you already did
return this.getUserProfileWithHttpCall();

);



user

UserProfile

this.getUserProfileWithHttpCall()

Promise<UserProfile>

getUserProfileWithHttpCall(): Observable<UserProfile >

Promise<UserProfile>

then

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