Скачать или смотреть Overcoming the Challenge of Iterating Over document.getElementsByClassName() in JavaScript

Discover how to successfully iterate over elements returned by `document.getElementsByClassName()` in JavaScript, fixing common issues.
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This video is based on the question https://stackoverflow.com/q/76641301/ asked by the user 'Harsh Kasodariya' ( https://stackoverflow.com/u/16496244/ ) and on the answer https://stackoverflow.com/a/76641340/ provided by the user 'kevP-Sirius' ( https://stackoverflow.com/u/11846725/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Challenge: Iterating Over document.getElementsByClassName()

As a JavaScript developer, you may encounter moments of confusion—especially when trying to manipulate elements on a web page. One such challenge is iterating over the elements retrieved using document.getElementsByClassName(). This method should return a live HTMLCollection of all elements that have the specified class name. However, you might find that the output behaves unexpectedly—such as displaying a length of 0, even when elements appear to be logged in the console.

The Problem in Detail

You’ve written code to access elements using document.getElementsByClassName(), only to find that the length of the returned collection is 0, even though visually it seems there are elements present. Here’s a breakdown of the scenario:

You have elements with the class name "brute-force-effect."

You log the output of your function and see the elements listed; however, when you check the length or try to iterate over them, it results in no outputs.

Example of the Problematic Code:

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

Attempting to iterate:

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

The confusion here might stem from when the code is executed in relation to the document's loading state.

Solution: Ensure Correct Execution Timing

The common culprit for this issue lies in when your code runs relative to the document's loading phase. If you attempt to access elements before the document has fully loaded, your script may not find them, leading to unexpected results like a length of 0.

Using DOMContentLoaded

To resolve this, you can wrap your code in a DOMContentLoaded event listener. This event triggers when the initial HTML document has been completely loaded and parsed, potentially ensuring the elements are available for manipulation.

Here’s How to Implement It:

Wrap your code within the event listener:

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

Why It Works

By placing your logic inside the DOMContentLoaded event listener:

You guarantee that the script runs after all resources (like HTML elements) have been completely loaded.

This approach prevents issues related to accessing elements that haven’t yet been rendered in the DOM.

Key Takeaways

Always ensure your JavaScript manipulates the DOM only after it has been completely loaded.

Use event listeners effectively to manage the timing of your DOM access.

If you encounter unexpected results like a length of 0 when accessing collections through document.getElementsByClassName(), check your code's execution context.

By following these steps and understanding the timing of your code execution, you can can confidently navigate and manipulate the DOM with JavaScript.