Скачать или смотреть How to Ensure jQuery Waits for a Return Value from Async Functions

Discover how to effectively use asynchronous functions in jQuery to ensure your code waits for a return value. Learn about Promises and the asynchronous keyword for smooth execution.
---
This video is based on the question https://stackoverflow.com/q/74393925/ asked by the user 'nikhil' ( https://stackoverflow.com/u/1852526/ ) and on the answer https://stackoverflow.com/a/74394227/ provided by the user 'Sergey Sosunov' ( https://stackoverflow.com/u/5767872/ ) 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: jQuery not waiting for the return value of the function

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.
---
Understanding jQuery's Asynchronous Nature: Solving the "Not Waiting" Problem

As developers, one of the common challenges we face when working with JavaScript and libraries like jQuery is effectively managing asynchronous operations. A prevalent issue arises when functions that rely on asynchronous calls do not behave as expected, specifically when you want to ensure that a piece of code executes only after an async operation has completed. In this post, we'll address a scenario in which a function needs to wait for the result of another function before proceeding, and how to solve it using Promises and the async/await syntax.

The Problem

In this case, we have two functions: IsValidEmail and PostComment. The function IsValidEmail checks if an email address is valid by making an asynchronous GET request to an external API. The function PostComment, on the other hand, is designed to process a form submission. However, it doesn't wait for IsValidEmail to complete before continuing its execution. This leads to a situation where alerts are displayed in the wrong order, causing confusion and errors in validation.

Here's a Breakdown of the Current Flow:

Alert for form validation failure: The alert for invalid form input appears first, confusing the user.

Alert with email validation status: The second alert presents the result of the email validation.

Final Alert: A third alert indicates that the email is valid.

This flow is problematic as the program should prioritize getting the validation status from IsValidEmail before deciding whether to proceed with form submission.

The Solution: Using Promises and Async/Await

To resolve this issue, we must adapt our approach by using Promises. This change allows us to handle asynchronous requests effectively and ensures that we can retrieve a return value from our asynchronous function.

Step 1: Modify IsValidEmail Function

We need to update the IsValidEmail function to return a Promise. This can be done by wrapping the jQuery $.get() call in a Promise, which will resolve with either true or false based on the email validation result.

Here's how the revised IsValidEmail function looks:

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

Step 2: Update PostComment Function

Next, we make the PostComment function asynchronous using the async keyword. Inside this function, we can then use the await keyword to pause execution until the Promise from IsValidEmail resolves.

Here’s the updated PostComment function:

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

Conclusion

By leveraging the power of Promises and the async/await syntax, we have transformed our code into a more robust structure that effectively waits for the completion of asynchronous functions. This approach ensures that the application's logic flows smoothly, providing a better user experience by guaranteeing that email validation occurs before any errors are reported or comments are submitted.

Now you can implement similar patterns in your own code to handle asynchronous calls with confidence!