Скачать или смотреть How to Wait for API Calls in a For Loop in Angular

Learn how to effectively manage asynchronous API calls in Angular using `async/await` and Observables for a smoother user experience.
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How to Wait for API Calls in a For Loop in Angular

Managing asynchronous operations, especially with API calls, can be tricky in Angular. If you find yourself needing to wait between API calls when processing multiple records in a for loop, you're not alone! In this guide, we will explore how to handle this using async/await along with Observables in Angular.

The Problem

You may have encountered a scenario where you need to perform an operation on multiple selected rows from a table (like an ag-grid). Each operation involves multiple API calls, and you want to ensure that the next operation doesn't begin until a set delay after the previous one completes. However, simply adding a setTimeout function often won’t provide the desired effect due to the nature of asynchronous programming.

Common Setup

Here’s what a typical setup might look like, where we attempt to run a Swap method for each selected record with a for loop:

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The Challenge

The above approach might not effectively wait for the given delay because setTimeout doesn’t stop the execution of the loop. Instead, we want to ensure that after each operation, the script pauses for a set duration before proceeding to the next iteration.

The Solution

To correctly implement a waiting mechanism between your API calls in Angular, you should leverage Observables along with lastValueFrom to await the completion of each API call. Here's how to structure your method effectively.

Step-by-Step Solution

Modify the SwapOrder Method:
Adjust this method to return an Observable rather than just making API calls directly.

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Use lastValueFrom in onSwap Method:
Changes should be made to your onSwap method to await the completion of the SwapOrder method and pause execution after each iteration.

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

Key Takeaways

Using Observables: The SwapOrder function now returns an Observable that allows chaining of multiple API calls.

Pausing Execution: By using lastValueFrom(timer(3000)), we can effectively introduce a delay between the operations.

User Feedback: Ensure your alerts or UI updates only occur after all necessary operations are completed within each iteration, creating a smoother user experience.

Conclusion

Managing multiple API calls in a loop can become complex, especially when requiring pauses between calls. By transforming your approach to leverage Observables and lastValueFrom, you can simplify the control flow while providing a responsive user experience.

Now, when you implement your API calls within a loop, you can ensure that each call completes and pauses as needed before moving to the next iteration.

Happy coding!