Solving the undefined Issue with Async/Await and Ajax in JavaScript

Dive deep into understanding why using `async/await` with jQuery's Ajax can lead to undefined returns and how to effectively fix it.
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This video is based on the question https://stackoverflow.com/q/68846794/ asked by the user 'Ben123' ( https://stackoverflow.com/u/11853066/ ) and on the answer https://stackoverflow.com/a/68846869/ provided by the user 'Bravo' ( https://stackoverflow.com/u/10549313/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the undefined Issue with Async/Await and Ajax

As you dive into the world of asynchronous programming in JavaScript, you may come across situations where using async/await with jQuery's Ajax functions can lead to some unexpected issues. One common problem developers face is that their async functions return undefined when they expect a value. This guide will explain why this happens and how you can resolve it effectively.

The Problem

Consider a scenario where you have an async function that checks if a business is currently open based on data fetched through an Ajax call:

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

You might call this isOpen function from another async function like this:

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

Despite using await, you find that open1 is always undefined. Why is that?

The Cause of the Problem

The main issue stems from how jQuery.ajax works with the .done method. Here’s why you’re getting undefined:

The data.done() callback is asynchronous and it runs after the initial execution of isOpen function has completed and returned. By the time return open; is reached, the Ajax call is likely still in progress, hence open may not have a value assigned yet.

As a result, the open variable has not been properly set before its value is returned, which causes it to be undefined.

The Solution

To fix this problem, we need to ensure that we handle the Ajax request correctly with await. Here’s how you can modify your isOpen function:

1. Use await with Ajax

Instead of using .done, leverage the await keyword directly with the $.ajax call:

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

2. Simplified Check Using .some() Method

You can also simplify the logic using the .some() method, which checks if at least one element in the array matches the condition:

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

Conclusion

The confusion surrounding undefined return values when using async/await with jQuery's Ajax calls is a common pitfall for many JavaScript developers. By waiting for the Ajax call to resolve with await, you can ensure that your function will return the expected results.

Feel free to implement these changes in your code and eliminate the undefined issue related to Ajax calls in JavaScript applications. This knowledge will help you write cleaner and more efficient asynchronous code.