Executing asynchronous function in Angular using Typescript

Question

Executing asynchronous function in Angular using Typescript

My team and I are new to Angular and we are facing a challenge with invoking methods in sequence and returning a value. The issue is that the return statement is being executed before the completion of the execution process. We have tried various approaches such as async/await, promises, setTimeout but have not been successful. Is there a solution available for ensuring synchronous order in Angular?

transform(input:any)
{

    this.getCachedUsers(); // This method sets the CachedUsers array using an HTTP GET call (subscribe)
    this.getUserFromCachedUsers(input); // This method sets the userName based on the input userID from CachedUsers
    return this.userName; // At this point, it's returning empty
}

javascript angular typescript angular-promise

Answer 1

Answer №1

If you want to enhance your Observable handling skills, consider exploring the world of observable flat operators.

One useful operator to check out is concatMap. It allows you to transform items emitted by an Observable into another Observable after the completion of the previous one. This creates an inner Observable and merges its results with the outer stream.

const source = this.getCachedUsers()
    .pipe(
        concatMap(result => this.getUserFromCachedUsers(result.userId))
     )
    .subscribe(result2 => {
        // perform some actions
    });

Here are several other flat operators that offer different functionalities:

flatMap/mergeMap - generates an Observable immediately for each source item, maintaining all previous Observables
concatMap - waits for the previous Observable to finish before creating the next one
switchMap - completes the previous Observable and starts a new one immediately for any source item
exhaustMap - maps to the inner observable, ignoring other values until that specific observable finishes

Answer 2

If you want to enhance your Observable handling skills, consider exploring the world of observable flat operators.

One useful operator to check out is concatMap. It allows you to transform items emitted by an Observable into another Observable after the completion of the previous one. This creates an inner Observable and merges its results with the outer stream.

const source = this.getCachedUsers()
    .pipe(
        concatMap(result => this.getUserFromCachedUsers(result.userId))
     )
    .subscribe(result2 => {
        // perform some actions
    });

Here are several other flat operators that offer different functionalities:

flatMap/mergeMap - generates an Observable immediately for each source item, maintaining all previous Observables
concatMap - waits for the previous Observable to finish before creating the next one
switchMap - completes the previous Observable and starts a new one immediately for any source item
exhaustMap - maps to the inner observable, ignoring other values until that specific observable finishes

Executing asynchronous function in Angular using Typescript

Answer №1

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