Скачать или смотреть Solving the random output issue in JS when looping through API fetches

Learn how to streamline the output of your JavaScript fetch calls through ordered execution so channels load in the correct sequence.
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This video is based on the question https://stackoverflow.com/q/65067920/ asked by the user 'Ginfio' ( https://stackoverflow.com/u/14629008/ ) and on the answer https://stackoverflow.com/a/65068021/ provided by the user 'Naga Raj' ( https://stackoverflow.com/u/11474426/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the random output issue in JS when looping through API fetches

When working with asynchronous operations in JavaScript, it’s common to run into issues where output appears in a seemingly random order. This can be especially perplexing when fetching data from APIs. In this guide, we’ll explore a situation faced by many developers—retrieving subscriber counts from YouTube channels and why the output might not reflect the intended order. We’ll also provide a clear solution to ensure the results are fetched in a specific sequence. Let’s dig in!

The Problem: Random Output Order

Imagine you're fetching subscriber counts from multiple YouTube channels using their API. You use an array to specify the channels, but when you log the subscriber counts, the values show up in a haphazard order. Here’s why this happens:

Asynchronous Fetching: JavaScript executes fetch requests asynchronously, which means they don’t wait for one to finish before starting the next. As a result, whichever fetch call responds fastest determines the order in which results are logged.

Index-Based Inconsistency: Because of this non-blocking behavior, outputs are printed based on the request that completes first, not on the order you specified in your channels array.

Here's the code that demonstrates this situation:

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

The Desired Outcome

What we want is for the channels to load in the order they appear in the channels array. Specifically:

Channel 1's data should load first

Channel 2's data should load second

Channel 3's data should load third

And so on...

The Solution: Using Async/Await

The best way to ensure that your fetch calls execute in the desired order is through the use of async/await. This way, you can pause the execution of code until the promise resolves, effectively making each fetch call happen sequentially.

Here’s how to modify the code using async/await:

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

Key Changes

Function Declaration: The function is declared as async, which allows the use of await within it.

Await Fetch Calls: By adding await before the fetch call, we ensure the current iteration of the loop will wait for the fetch to complete before moving to the next channel.

Conclusion

By utilizing async/await, you can significantly improve the readability and functionality of your JavaScript code, ensuring that data retrieved from API calls respects the order defined in your arrays. No longer will you be left wondering why your results appear randomly—now they'll display in the intended sequence! Happy coding!