HTMLCollection vs. NodeList: Why Does Modifying an HTMLCollection\'s Elements Affect Its Size?

HTMLCollection vs. NodeList: The Root of the Problem

The script presented encounters a problem due to the fact that it manipulates an HTMLCollection rather than a NodeList to modify CSS classes. An HTMLCollection is a live collection, meaning that its contents automatically update as changes are made to the DOM (Document Object Model). This behavior leads to the unintended consequence of altering the collection's size as elements' class names are modified. Each time an element has its class name changed, the collection excludes that element, resulting in a decrease in its size.

The Solution: Iterating Over Only the First Element

To address this issue, it is crucial to understand that altering the class name of any element within the collection affects the collection itself. The optimal solution, therefore, is to modify the class name of only the first element, ensuring that the collection's size remains constant.

For Loop for Class Name Modification

Instead of manually changing the class names of multiple elements, the script can iterate through each element in the HTMLCollection using a for loop. This approach allows for consistent class name modification without affecting the collection's size.

Enhanced Code Example

The modified code employs a for loop to iterate through the HTMLCollection and change the class name of each element to "block-selected":

var blockSet = document.getElementsByClassName("block-default");
var blockSetLength = blockSet.length;

for(var i = 0; i < blockSetLength; i++) {
    blockSet[0].className = "block-selected";
}

Conclusion

Understanding the distinction between HTMLCollections and NodeLists is essential in JavaScript programming. By utilizing the correct data structure for the task at hand, developers can avoid unintended consequences and achieve the desired outcomes efficiently.

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