# Interface NamedNodeMap

public interface NamedNodeMap
Objects implementing the `NamedNodeMap` interface are used to represent collections of nodes that can be accessed by name. Note that `NamedNodeMap` does not inherit from `NodeList`; `NamedNodeMaps` are not maintained in any particular order. Objects contained in an object implementing `NamedNodeMap` may also be accessed by an ordinal index, but this is simply to allow convenient enumeration of the contents of a `NamedNodeMap`, and does not imply that the DOM specifies an order to these Nodes.

`NamedNodeMap` objects in the DOM are live.

See also the Document Object Model (DOM) Level 3 Core Specification.

Since:
  1.4, DOM Level 2

- ## Method Summary

  Modifier and Type
  Method
  Description
  `int`
  `getLength()`
  The number of nodes in this map.
  `Node`
  `getNamedItem(String name)`
  Retrieves a node specified by name.
  `Node`
  `getNamedItemNS(String namespaceURI, String localName)`
  Retrieves a node specified by local name and namespace URI.
  `Node`
  `item(int index)`
  Returns the `index`th item in the map.
  `Node`
  `removeNamedItem(String name)`
  Removes a node specified by name.
  `Node`
  `removeNamedItemNS(String namespaceURI, String localName)`
  Removes a node specified by local name and namespace URI.
  `Node`
  `setNamedItem(Node arg)`
  Adds a node using its `nodeName` attribute.
  `Node`
  `setNamedItemNS(Node arg)`
  Adds a node using its `namespaceURI` and `localName`.

- ## Method Details

  - ### getNamedItem

    Node getNamedItem(String name)
    Retrieves a node specified by name.
    Parameters:
      `name` - The `nodeName` of a node to retrieve.
    Returns:
      A `Node` (of any type) with the specified `nodeName`, or `null` if it does not identify any node in this map.

  - ### setNamedItem

    Node setNamedItem(Node arg) throws DOMException
    Adds a node using its `nodeName` attribute. If a node with that name is already present in this map, it is replaced by the new one. Replacing a node by itself has no effect.
    As the `nodeName` attribute is used to derive the name which the node must be stored under, multiple nodes of certain types (those that have a "special" string value) cannot be stored as the names would clash. This is seen as preferable to allowing nodes to be aliased.
    Parameters:
      `arg` - A node to store in this map. The node will later be accessible using the value of its `nodeName` attribute.
    Returns:
      If the new `Node` replaces an existing node the replaced `Node` is returned, otherwise `null` is returned.
    Throws:
      `DOMException` - WRONG_DOCUMENT_ERR: Raised if `arg` was created from a different document than the one that created this map.
      NO_MODIFICATION_ALLOWED_ERR: Raised if this map is readonly.
      INUSE_ATTRIBUTE_ERR: Raised if `arg` is an `Attr` that is already an attribute of another `Element` object. The DOM user must explicitly clone `Attr` nodes to re-use them in other elements.
      HIERARCHY_REQUEST_ERR: Raised if an attempt is made to add a node doesn't belong in this NamedNodeMap. Examples would include trying to insert something other than an Attr node into an Element's map of attributes, or a non-Entity node into the DocumentType's map of Entities.

  - ### removeNamedItem

    Node removeNamedItem(String name) throws DOMException
    Removes a node specified by name. When this map contains the attributes attached to an element, if the removed attribute is known to have a default value, an attribute immediately appears containing the default value as well as the corresponding namespace URI, local name, and prefix when applicable.
    Parameters:
      `name` - The `nodeName` of the node to remove.
    Returns:
      The node removed from this map if a node with such a name exists.
    Throws:
      `DOMException` - NOT_FOUND_ERR: Raised if there is no node named `name` in this map.
      NO_MODIFICATION_ALLOWED_ERR: Raised if this map is readonly.

  - ### item

    Node item(int index)
    Returns the `index`th item in the map. If `index` is greater than or equal to the number of nodes in this map, this returns `null`.
    Parameters:
      `index` - Index into this map.
    Returns:
      The node at the `index`th position in the map, or `null` if that is not a valid index.

  - ### getLength

    int getLength()
    The number of nodes in this map. The range of valid child node indices is `0` to `length-1` inclusive.

  - ### getNamedItemNS

    Node getNamedItemNS(String namespaceURI, String localName) throws DOMException
    Retrieves a node specified by local name and namespace URI.
    Per [XML Namespaces] , applications must use the value null as the namespaceURI parameter for methods if they wish to have no namespace.
    Parameters:
      `namespaceURI` - The namespace URI of the node to retrieve.
      `localName` - The local name of the node to retrieve.
    Returns:
      A `Node` (of any type) with the specified local name and namespace URI, or `null` if they do not identify any node in this map.
    Throws:
      `DOMException` - NOT_SUPPORTED_ERR: May be raised if the implementation does not support the feature "XML" and the language exposed through the Document does not support XML Namespaces (such as [HTML 4.01]).
    Since:
      1.4, DOM Level 2

  - ### setNamedItemNS

    Node setNamedItemNS(Node arg) throws DOMException
    Adds a node using its `namespaceURI` and `localName`. If a node with that namespace URI and that local name is already present in this map, it is replaced by the new one. Replacing a node by itself has no effect.
    Per [XML Namespaces] , applications must use the value null as the namespaceURI parameter for methods if they wish to have no namespace.
    Parameters:
      `arg` - A node to store in this map. The node will later be accessible using the value of its `namespaceURI` and `localName` attributes.
    Returns:
      If the new `Node` replaces an existing node the replaced `Node` is returned, otherwise `null` is returned.
    Throws:
      `DOMException` - WRONG_DOCUMENT_ERR: Raised if `arg` was created from a different document than the one that created this map.
      NO_MODIFICATION_ALLOWED_ERR: Raised if this map is readonly.
      INUSE_ATTRIBUTE_ERR: Raised if `arg` is an `Attr` that is already an attribute of another `Element` object. The DOM user must explicitly clone `Attr` nodes to re-use them in other elements.
      HIERARCHY_REQUEST_ERR: Raised if an attempt is made to add a node doesn't belong in this NamedNodeMap. Examples would include trying to insert something other than an Attr node into an Element's map of attributes, or a non-Entity node into the DocumentType's map of Entities.
      NOT_SUPPORTED_ERR: May be raised if the implementation does not support the feature "XML" and the language exposed through the Document does not support XML Namespaces (such as [HTML 4.01]).
    Since:
      1.4, DOM Level 2

  - ### removeNamedItemNS

    Node removeNamedItemNS(String namespaceURI, String localName) throws DOMException
    Removes a node specified by local name and namespace URI. A removed attribute may be known to have a default value when this map contains the attributes attached to an element, as returned by the attributes attribute of the `Node` interface. If so, an attribute immediately appears containing the default value as well as the corresponding namespace URI, local name, and prefix when applicable.
    Per [XML Namespaces] , applications must use the value null as the namespaceURI parameter for methods if they wish to have no namespace.
    Parameters:
      `namespaceURI` - The namespace URI of the node to remove.
      `localName` - The local name of the node to remove.
    Returns:
      The node removed from this map if a node with such a local name and namespace URI exists.
    Throws:
      `DOMException` - NOT_FOUND_ERR: Raised if there is no node with the specified `namespaceURI` and `localName` in this map.
      NO_MODIFICATION_ALLOWED_ERR: Raised if this map is readonly.
      NOT_SUPPORTED_ERR: May be raised if the implementation does not support the feature "XML" and the language exposed through the Document does not support XML Namespaces (such as [HTML 4.01]).
    Since:
      1.4, DOM Level 2