getNamespaceURI

getNamespaceURI is a function of the Document Object Model (DOM) API that returns the namespace URI associated with a given node. It is primarily used in the context of XML namespaces to identify the namespace in which a node resides, enabling disambiguation of elements and attributes that share a local name but belong to different namespaces.

The method returns a string containing the namespace URI, or null if the node has no namespace or if namespaces are not used for that node. It applies to nodes that participate in namespaces, such as Element and Attr nodes; for nodes that do not have a namespace (for example, certain text or comment nodes), the result is typically null. The value reflects the namespace declared for the node in the document, not necessarily the prefix used in the document.

In practice, elements and attributes created or parsed with namespace awareness carry a non-null namespaceURI, obtained either from the source document or by using createElementNS and related methods. The related getPrefix method can be used to retrieve the namespace prefix, if any, that was associated with the node's namespace. Namespace handling and getNamespaceURI are defined by the XML Namespaces specification and are part of the DOM’s support for namespace-aware documents.

In web browsers, the equivalent property on DOM nodes is namespaceURI, accessed directly as a property in JavaScript. In languages such as Java, the corresponding API provides getNamespaceURI() as a method. Use of this value is common in XML processing, XPath queries, and in logic that differentiates nodes by namespace rather than by local name alone.