TagName

tagName is a property of element nodes in the Document Object Model (DOM) that exposes the name of the element’s tag. It is commonly used to identify or compare elements by their tag type and to drive logic based on element kinds. The value is a string derived from the element’s name in the source markup.

In HTML documents, the tagName property typically returns the tag name in uppercase (for example, "DIV" or "SPAN"). It is read-only and reflects the element’s nominal tag. In most browsers this property does not include namespace information, which distinguishes it from other name-related properties.

In XML and XML-based documents, tagName reflects the element’s qualified name, which may include a namespace prefix (for example, "ns:tag"). XML parsing is generally case-sensitive, so tagName preserves the case as written. The localName property can be used to retrieve just the local part of the name, separately from its namespace prefix, and namespaceURI provides the namespace URI.

Common usage involves identifying elements by tag name, often with methods such as getElementsByTagName or, more recently, querySelectorAll, to select elements with a given tag. tagName can also be used in conditional logic or in loops when processing elements of specific types.

Related concepts include localName and namespaceURI for namespace-aware documents, and the methods used to select elements by tag name, such as getElementsByTagName and querySelectorAll.