How to Use rxjs to Chain API Calls in Angular with Observables

Learn how to efficiently manage multiple API calls in Angular using `rxjs`, merging data from one observable into another.
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This video is based on the question https://stackoverflow.com/q/66186345/ asked by the user 'Johnczek' ( https://stackoverflow.com/u/6073577/ ) and on the answer https://stackoverflow.com/a/66186535/ provided by the user 'Quentin Grisel' ( https://stackoverflow.com/u/9868549/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use rxjs to Chain API Calls in Angular with Observables

In today's web applications, handling multiple API calls effectively can significantly improve user experience. If you're working with Angular, you've likely encountered scenarios where the output of one API call needs to feed into another. This is where rxjs becomes incredibly useful, allowing you to combine and manipulate observables seamlessly.

In this guide, we'll tackle a specific case involving two API endpoints:

EP-A - Uploading a user avatar.

EP-B - Updating the user's profile with the uploaded avatar's UUID.

The Problem

You need to perform two sequential API calls:

Call EP-A with a blob containing the avatar image. This call returns a response containing a uuid.

Call EP-B immediately after, using the returned uuid to update the user's profile.

If either call fails, you want to present an appropriate error message to the user.

Here's a simplified version of the method you currently have, which needs enhancement to connect the two observables efficiently.

Current Method Structure

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

The Solution

The ideal approach to connect the two calls is by using the pipe() method provided by rxjs. This allows you to chain operators like mergeMap or flatMap and manage the asynchronous flow of your API calls. Here's how you can implement it:

Step-by-Step Implementation

Use pipe() to Chain API Calls - By utilizing the pipe() method with mergeMap or flatMap, you can easily manage the flow from one observable to another.

Handle Responses - Utilize the operators tap() to perform side effects (like logging) and catchError() to handle potential errors.

Complete Implementation Example

Here’s how you can refactor your method to use rxjs effectively:

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

Breaking Down the Implementation

mergeMap Operator: This operator allows you to take the result of the first API call and emit the observable returned from the second API call, effectively chaining them.

tap Operator: Useful for performing side effects, like logging without affecting data flow.

catchError Operator: Catches any errors during the API calls and allows you to handle them gracefully.

Conclusion

By using rxjs, merging observables from different API calls becomes straightforward. This approach not only enhances your application’s efficiency but also handles errors more gracefully, improving the overall user experience.

Now that you have the tools and strategies at your disposal, you can tackle your projects with confidence, knowing how to effectively manage asynchronous operations in Angular!

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