The read-only firstChild property of the Node interface returns the node's first child in the tree, or null if the node has no children.

If the node is a Document, this property returns the first node in the list of its direct children.

A Node, or null if there are none.

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>

<script>
  const p01 = document.getElementById("para-01");
  console.log(p01.firstChild.nodeName);
</script>

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>

<script>
  const p01 = document.getElementById("para-01");
  console.log(p01.firstChild.nodeName);
</script>

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.

• Element.firstElementChild
• Node.lastChild