The tagName read-only property of the Element interface returns the tag name of the element on which it's called.

For example, if the element is an <img>, its tagName property is "IMG" (for HTML documents; it may be cased differently for XML/XHTML documents).

A string indicating the element's tag name. This string's capitalization depends on the document type:

• For DOM trees which represent HTML documents, the returned tag name is always in the canonical upper-case form. For example, tagName called on a <div> element returns "DIV".
• The tag names of elements in an XML DOM tree are returned in the same case in which they're written in the original XML file. If an XML document includes a tag "<SomeTag>", then the tagName property's value is "SomeTag".

For Element objects, the value of tagName is the same as the value of the nodeName property the element object inherits from Node.

const span = document.getElementById("born");
console.log(span.tagName);

In XHTML (or any other XML format), the original case will be maintained, so "span" would be output in case the original tag name was created lowercase. In HTML, "SPAN" would be output instead regardless of the case used while creating the original document.