Скачать или смотреть Efficiently Handling Async and Sync API Calls in JavaScript

Learn how to manage two looped async API calls followed by a sync call in JavaScript, ensuring proper order of operations and error handling.
---
This video is based on the question https://stackoverflow.com/q/63981000/ asked by the user 'keanu' ( https://stackoverflow.com/u/8339906/ ) and on the answer https://stackoverflow.com/a/63981050/ provided by the user 'CertainPerformance' ( https://stackoverflow.com/u/9515207/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Two looped async calls followed by a sync call

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Efficiently Handling Two Looped Async API Calls Followed by a Sync Call

In the world of JavaScript, particularly when dealing with React applications, it’s common to encounter scenarios involving asynchronous operations. One such scenario arises when we need to edit previously saved messages that contain attachments. This guide will explain how to manage two async API calls that deal with replacement and deletion of attachments, followed by a synchronous API call to save changes to the message text.

The Problem

Imagine this situation: a user wants to edit a message by changing its title or text, replacing an existing attachment, and deleting two other attachments. Once they hit the Save button, three main actions should take place:

Async API calls to replace and delete attachments.

Once these operations are successful, a sync call to save the modified message text.

However, the issue arises because the Promise.all structure used to manage these operations can result in the outer promise resolving prematurely if not handled correctly.

Understanding the Current Implementation

The current implementation involves defined functions to handle deletion, replacement, and saving of the message:

Functions Overview

Delete Function

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

Replace Function

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

Save Message Function

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

Handle Save Function

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

The current way of implementing Promise.all incorrectly wraps the .map() function in an array, causing it to resolve immediately without waiting for the promises inside to complete.

The Solution

To ensure that the two async API calls finish before proceeding to save the message text, we need to modify the promise structures to pass an array of promises properly. Here’s how to resolve the issues in the code:

Correcting the Promise.all Usage

Instead of wrapping the .map() in an array, do the following:

Modification for Delete Function
Update the delete function like this:

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

Modification for Replace Function
Similarly, the replace function should be modified:

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

Handling Errors Properly

When dealing with potential errors, especially HTTP 400 errors, ensure that your promises reject properly:

Replace Function Error Handling
Change:

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

To:

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

Ensuring Save Message Function Returns Promises

Finally, don’t forget to return the promise from the saveMessage function so that any errors are captured in the catch block of the handleSave function:

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

Final Implementation

With these changes made, the revised handleSave function will look like this:

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

Conclusion

By managing asynchronous calls correctly and handling error states effectively, you can ensure that operations like editing messages and attachments in a React application proceed smoothly and reliably. This approach not only results in fewer bugs but also provides a better user experience.

Теперь, во время следующего редактирования сообщений, вы сможете гарантировать, что все запросы будут завершены в правильной последовательности, прежде чем обновить текст сообщения!

Remember, asynchronous programming can be tricky, but with the right structure, it becomes much simpler!