This example demonstrates the use of firstChild and how whitespace nodes might interfere with using this property.
<p id="para-01">
<span>First span</span>
</p>
const p01 = document.getElementById("para-01");
console.log(p01.firstChild.nodeName);
In the above, the console will show '#text' because a text node is inserted to maintain the whitespace between the end of the opening <p> and <span> tags. Any whitespace will create a #text node, from a single space to multiple spaces, returns, tabs, and so on.
Another #text node is inserted between the closing </span> and </p> tags.
If this whitespace is removed from the source, the #text nodes are not inserted and the span element becomes the paragraph's first child.
<p id="para-01"><span>First span</span></p>
const p01 = document.getElementById("para-01");
console.log(p01.firstChild.nodeName);
Now the console will show 'SPAN'.
To avoid the issue with node.firstChild returning #text or #comment nodes, Element.firstElementChild can be used to return only the first element node.
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