Wait for API Call Completion in Angular: Making Your Subscriptions Work Together

Learn how to manage multiple API calls in Angular with RxJS, ensuring that each call waits for the previous one to finish.
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Wait for API Call Completion in Angular

When working with asynchronous API calls in Angular, it's common to encounter issues where multiple subscriptions execute in parallel without waiting for one another. This can lead to a number of problems, such as failed API calls or unintended behaviors in your application. In this guide, we'll discuss how to properly manage your subscriptions so that API calls wait for each other to complete before proceeding.

The Problem

Imagine you have a scenario where you want to create a customer and, once that's done, subsequently create various associated records (like an address and contact details).

However, if your API calls are structured to run concurrently, you may quite easily encounter failures. This is particularly evident when you inspect the network tab in Chrome and see that an API call to create the customer hasn't finished executing before other calls (like creating an address and a phone number) start firing off.

Encountering API Call Failures

You might have encountered something like this:

Your first API call succeeds, but the associated calls fail because they rely on data from the first call which isn’t yet available.

You look for solutions, but older patterns like using await....toPromise() are deprecated in modern Angular and RxJS.

So, how do you implement a solution that works in the latest versions of these libraries?

The Solution: Utilizing RxJS Operators

Fortunately, there are powerful operators in RxJS such as switchMap and mergeMap that can help coordinate your asynchronous calls effectively. This way, you won't nest your subscriptions and can instead return observables directly.

Step-by-Step Implementation

Here’s how to structure your API calls correctly:

Create the Customer: Initiate your first API call using the createCustomer method.

Chain Additional Calls: Use switchMap to only proceed with additional calls once the first one completes.

Combine the Results: When you have additional data to create (like addresses or emails), use operators like combineLatestWith to ensure all calls complete before persisting data.

Handle Responses: Subscribe to the final callable to manage responses and potential errors effectively.

Example Code

Here’s an example code snippet to illustrate this:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code

switchMap: This operator is crucial as it switches to the observable returned from the API call to create the address only after the customer is created.

combineLatestWith: This allows you to combine multiple observables, ensuring that the operation only continues once all API calls have returned their results.

Error Handling: Manage potential errors gracefully to provide a better user experience.

Conclusion

By effectively using RxJS operators like switchMap and combineLatestWith, you can manage complex logic in your Angular applications without falling prey to the pitfalls of fast-firing asynchronous code. Ensure that your API calls are executed sequentially, preventing any potential race conditions and ultimately leading to a smoother user experience.

If you have any questions or need further assistance with similar issues in your Angular applications, feel free to reach out!