Скачать или смотреть Understanding getElementsByClassName Strange Behavior: A Better Solution with querySelectorAll

Discover why `getElementsByClassName` may skip elements and learn how to use `querySelectorAll` for reliable results in JavaScript
---
This video is based on the question https://stackoverflow.com/q/64980976/ asked by the user 'MysteryPancake' ( https://stackoverflow.com/u/6931415/ ) and on the answer https://stackoverflow.com/a/64981052/ provided by the user 'mplungjan' ( https://stackoverflow.com/u/295783/ ) 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: getElementsByClassName strange behavior, skipping certain elements

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 getElementsByClassName Strange Behavior

When working on JavaScript, developers often rely on methods like getElementsByClassName to manipulate elements in their web applications. However, you might occasionally encounter some strange behavior, like "skipping" certain elements. In this guide, we'll explore this issue and provide a clear solution to how you can effectively manage class swapping between elements.

The Problem: Unpredictable Class Swapping

Let’s illustrate the issue with a common scenario. Imagine you have multiple HTML elements with a specific class, say class classb, and you want to change them to another class, classa. You might expect every instance of classb to be converted to classa, but your JavaScript code might only swap some of them, leading to confusion and frustration. Here’s a simplified version of the JavaScript function that exhibits this behavior:

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

Why Does This Happen?

The issue here stems from how getElementsByClassName works. It returns a "live" NodeList, which means that if you modify the elements in that list, the list will automatically update its length and contents. As you swap the classes in your loop, you inadvertently alter the list you're iterating over, which can lead to skipping elements.

The Solution: Using querySelectorAll

To overcome this strange behavior, we can rely on querySelectorAll, which returns a static NodeList (not live). This allows us to work with the elements without worrying about updating the list during our operations. Here’s how you can modify the function using querySelectorAll along with classList to swap classes more effectively:

Updated Code Example

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

Benefits of This Approach

Static NodeList: You avoid the complications that come with live NodeLists.

Readability and Maintenance: Using forEach makes your code cleaner and easier to understand.

Support for Older Browsers: If you need to support older versions of Edge or other browsers, remember to use the spread operator ([...]) to convert the NodeList to an Array like this:

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

Conclusion

Whether you're a seasoned developer or a beginner, encountering strange behavior with getElementsByClassName can be perplexing. However, by transitioning to querySelectorAll and making use of classList, you can build a more robust and reliable solution for managing classes in your web applications. This will not only improve your code’s performance but also enhance its maintainability.

With these tips in your toolbox, you're now ready to tackle similar issues confidently. Happy coding!