Understanding the Return Format of querySelectorAll('*') in JavaScript

I recently ran this line of code:

var elements = document.querySelectorAll(‘div *’);

Here, div refers to a generic div element, such as the one shown below:
<div>
<select>
<option>Option1</option>
<option>Option2</option>
<option>Option3</option>
<optgroup>
<option>GroupOption1</option>
<option>GroupOption2</option>
</optgroup>
</select>
</div>

My question is: what will the variable elements contain after executing this? Is there a standardized approach in JavaScript for this, or is it up to the individual implementations? Additionally, how does JavaScript navigate through the DOM nodes? Does it use a Depth-First Search (DFS) method that ensures a completely flattened structure of nodes?

When you run document.querySelectorAll('div *'), the elements variable will contain a NodeList of all descendant elements inside the div. It searches through the DOM using a preorder traversal, similar to Depth-First Search, returning nodes in document order.

So in your example, it will include the select, each option, and the optgroup tags.

The querySelectorAll('div *') method in JavaScript is particularly useful when you want to collect all the descendant elements of a specific parent element, in this case, a <div>. The result is a NodeList, which is a collection of nodes retrieved in the order they appear in the document, often mirroring the document tree structure.

When considering the DOM traversal mechanism, JavaScript uses a process resembling Depth-First Search (DFS) when executing the querySelectorAll method, ensuring it recursively explores the breadth of the DOM, targeting each child node before moving to sibling nodes. This approach effectively flattens the nested hierarchy of the elements within the selected div tag into a linear sequence (the NodeList), preserving the natural order from top to bottom as they are found in the HTML document.

In your specific example, the NodeList will contain:

  • <select> element
  • Each individual <option> element
  • The <optgroup> as a single node, followed by its child <option> nodes

This standardized approach in JavaScript is consistent across browser implementations, providing predictable behavior when querying elements. Remember, a NodeList is not an Array, but it can be traversed using methods like forEach for operations such as iterating over elements or converting them into an Array.

elements.forEach(node => console.log(node));

This code snippet will log each node within the NodeList, displaying their type and content, allowing for further exploration or manipulation as needed.