Скачать или смотреть Handling Conditional Calls in RxJS with concatMap

This guide explains how to handle conditional HTTP calls in Angular using `RxJS`'s `concatMap`. Learn error handling with `catchError` and implement checks before making secondary API calls for robust application performance.
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This video is based on the question https://stackoverflow.com/q/63114588/ asked by the user 'jaffer' ( https://stackoverflow.com/u/6689996/ ) and on the answer https://stackoverflow.com/a/63115197/ provided by the user 'Naveen Motwani - AIS' ( https://stackoverflow.com/u/1773354/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Managing Conditional API Calls with RxJS's concatMap

In the world of Angular and RxJS, dealing with multiple asynchronous operations is a common task. One frequent scenario developers encounter is the need to conditionally execute an API call based on the result of a previous call. In this post, we’ll delve into how to effectively execute a second HTTP call only if the first one succeeds.

The Problem: Conditional Execution of Calls

You might have come across a situation where you want to make an API call, check the result of that call, and if certain conditions are met, proceed to make a second API call. This is a typical requirement in many applications, but it can become complicated, especially when handling errors or unexpected results.

Example Scenario

Suppose you need to fetch user details with an API call and, based on the success of that call, proceed to submit a form. What if the first call fails? You need a way to handle that failure gracefully while ensuring that your application behaves as expected.

The Solution: Using concatMap and catchError

To implement this functionality, we can utilize RxJS operators such as concatMap and catchError. Below are the steps to achieve conditional API call execution.

Step 1: Initial API Call

First, start with your initial service call using the HttpClient. You can leverage Angular’s HttpClient to perform your GET request:

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Step 2: Using concatMap for Conditional Logic

Next, employ the concatMap operator. Inside this operator, we will check the result of the first API call and decide the next step. Here's how to structure it:

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Step 3: Handling Errors with catchError

It's essential to manage errors gracefully. You can use the catchError operator to catch any errors that arise from the first API call.

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Full Implementation Example

Here’s how the complete code would look:

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Conclusion

By leveraging RxJS operators like concatMap and catchError, you can create robust Angular applications that handle conditional API calls gracefully. This pattern not only ensures that your application remains responsive to user interactions but also helps in maintaining a clean separation of concerns in your code.

Now, next time you need to perform conditional API calls in your Angular app, you have the knowledge to do it efficiently!