The Attr interface represents an attribute in an Element object. Typically the allowable values for the attribute are defined in a schema associated with the document.

Attr objects inherit the Node interface, but since they are not actually child nodes of the element they describe, the DOM does not consider them part of the document tree. Thus, the Node attributes parentNode, previousSibling, and nextSibling have a null value for Attr objects. The DOM takes the view that attributes are properties of elements rather than having a separate identity from the elements they are associated with; this should make it more efficient to implement such features as default attributes associated with all elements of a given type. Furthermore, Attr nodes may not be immediate children of a DocumentFragment. However, they can be associated with Element nodes contained within a DocumentFragment. In short, users and implementors of the DOM need to be aware that Attr nodes have some things in common with other objects inheriting the Node interface, but they also are quite distinct.

The attribute's effective value is determined as follows: if this attribute has been explicitly assigned any value, that value is the attribute's effective value; otherwise, if there is a declaration for this attribute, and that declaration includes a default value, then that default value is the attribute's effective value; otherwise, the attribute does not exist on this element in the structure model until it has been explicitly added. Note that the Node.nodeValue attribute on the Attr instance can also be used to retrieve the string version of the attribute's value(s).

If the attribute was not explicitly given a value in the instance document but has a default value provided by the schema associated with the document, an attribute node will be created with specified set to false. Removing attribute nodes for which a default value is defined in the schema generates a new attribute node with the default value and specified set to false. If validation occurred while invoking Document.normalizeDocument(), attribute nodes with specified equals to false are recomputed according to the default attribute values provided by the schema. If no default value is associate with this attribute in the schema, the attribute node is discarded.

In XML, where the value of an attribute can contain entity references, the child nodes of the Attr node may be either Text or EntityReference nodes (when these are in use; see the description of EntityReference for discussion).

The DOM Core represents all attribute values as simple strings, even if the DTD or schema associated with the document declares them of some specific type such as tokenized.

The way attribute value normalization is performed by the DOM implementation depends on how much the implementation knows about the schema in use. Typically, the value and nodeValue attributes of an Attr node initially returns the normalized value given by the parser. It is also the case after Document.normalizeDocument() is called (assuming the right options have been set). But this may not be the case after mutation, independently of whether the mutation is performed by setting the string value directly or by changing the Attr child nodes. In particular, this is true when character references are involved, given that they are not represented in the DOM and they impact attribute value normalization. On the other hand, if the implementation knows about the schema in use when the attribute value is changed, and it is of a different type than CDATA, it may normalize it again at that time. This is especially true of specialized DOM implementations, such as SVG DOM implementations, which store attribute values in an internal form different from a string.

The following table gives some examples of the relations between the attribute value in the original document (parsed attribute), the value as exposed in the DOM, and the serialization of the value:
Examples Parsed attribute value Initial Attr.value Serialized attribute value
Character reference 
"x²=5"
 
"x²=5"
 
"x²=5"
Built-in character entity 
"y<6"
 
"y<6"
 
"y&lt;6"
Literal newline between 
 "x=5&#10;y=6"
 
"x=5 y=6"
 
"x=5&#10;y=6"
Normalized newline between 
"x=5 
 y=6"
 
"x=5 y=6"
 
"x=5 y=6"
Entity e with literal newline 
 <!ENTITY e '...&#10;...'> [...]> "x=5&e;y=6"
 Dependent on Implementation and Load Options Dependent on Implementation and Load/Save Options

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

The node is an Attr.
The node is a CDATASection.
The node is a Comment.
The node is a DocumentFragment.
The node is a Document.
The node is contained by the reference node. A node which is contained is always following, too.
The node contains the reference node. A node which contains is always preceding, too.
The two nodes are disconnected. Order between disconnected nodes is always implementation-specific.
The node follows the reference node.
The determination of preceding versus following is implementation-specific.
The second node precedes the reference node.
The node is a DocumentType.
The node is an Element.
The node is an Entity.
The node is an EntityReference.
The node is a Notation.
The node is a ProcessingInstruction.
The node is a Text node.
Adds the node newChild to the end of the list of children of this node. If the newChild is already in the tree, it is first removed.
Parameters
newChildThe node to add.If it is a DocumentFragment object, the entire contents of the document fragment are moved into the child list of this node
Return
The node added.
Throws
DOMException HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the newChild node, or if the node to append is one of this node's ancestors or this node itself, or if this node is of type Document and the DOM application attempts to append a second DocumentType or Element node.
WRONG_DOCUMENT_ERR: Raised if newChild was created from a different document than the one that created this node.
NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly or if the previous parent of the node being inserted is readonly.
NOT_SUPPORTED_ERR: if the newChild node is a child of the Document node, this exception might be raised if the DOM implementation doesn't support the removal of the DocumentType child or Element child.
@version
DOM Level 3
Returns a duplicate of this node, i.e., serves as a generic copy constructor for nodes. The duplicate node has no parent ( parentNode is null) and no user data. User data associated to the imported node is not carried over. However, if any UserDataHandlers has been specified along with the associated data these handlers will be called with the appropriate parameters before this method returns.
Cloning an Element copies all attributes and their values, including those generated by the XML processor to represent defaulted attributes, but this method does not copy any children it contains unless it is a deep clone. This includes text contained in an the Element since the text is contained in a child Text node. Cloning an Attr directly, as opposed to be cloned as part of an Element cloning operation, returns a specified attribute (specified is true). Cloning an Attr always clones its children, since they represent its value, no matter whether this is a deep clone or not. Cloning an EntityReference automatically constructs its subtree if a corresponding Entity is available, no matter whether this is a deep clone or not. Cloning any other type of node simply returns a copy of this node.
Note that cloning an immutable subtree results in a mutable copy, but the children of an EntityReference clone are readonly . In addition, clones of unspecified Attr nodes are specified. And, cloning Document, DocumentType, Entity, and Notation nodes is implementation dependent.
Parameters
deepIf true, recursively clone the subtree under the specified node; if false, clone only the node itself (and its attributes, if it is an Element).
Return
The duplicate node.
Compares the reference node, i.e. the node on which this method is being called, with a node, i.e. the one passed as a parameter, with regard to their position in the document and according to the document order.
Parameters
otherThe node to compare against the reference node.
Return
Returns how the node is positioned relatively to the reference node.
Throws
DOMException NOT_SUPPORTED_ERR: when the compared nodes are from different DOM implementations that do not coordinate to return consistent implementation-specific results.
@since
DOM Level 3
A NamedNodeMap containing the attributes of this node (if it is an Element) or null otherwise.
The absolute base URI of this node or null if the implementation wasn't able to obtain an absolute URI. This value is computed as described in . However, when the Document supports the feature "HTML" [DOM Level 2 HTML] , the base URI is computed using first the value of the href attribute of the HTML BASE element if any, and the value of the documentURI attribute from the Document interface otherwise.
@since
DOM Level 3
A NodeList that contains all children of this node. If there are no children, this is a NodeList containing no nodes.
This method returns a specialized object which implements the specialized APIs of the specified feature and version, as specified in . The specialized object may also be obtained by using binding-specific casting methods but is not necessarily expected to, as discussed in . This method also allow the implementation to provide specialized objects which do not support the Node interface.
Parameters
featureThe name of the feature requested. Note that any plus sign "+" prepended to the name of the feature will be ignored since it is not significant in the context of this method.
versionThis is the version number of the feature to test.
Return
Returns an object which implements the specialized APIs of the specified feature and version, if any, or null if there is no object which implements interfaces associated with that feature. If the DOMObject returned by this method implements the Node interface, it must delegate to the primary core Node and not return results inconsistent with the primary core Node such as attributes, childNodes, etc.
@since
DOM Level 3
The first child of this node. If there is no such node, this returns null.
The last child of this node. If there is no such node, this returns null.
Returns the local part of the qualified name of this node.
For nodes of any type other than ELEMENT_NODE and ATTRIBUTE_NODE and nodes created with a DOM Level 1 method, such as Document.createElement(), this is always null.
@since
DOM Level 2
Returns the name of this attribute. If Node.localName is different from null, this attribute is a qualified name.
The namespace URI of this node, or null if it is unspecified (see ).
This is not a computed value that is the result of a namespace lookup based on an examination of the namespace declarations in scope. It is merely the namespace URI given at creation time.
For nodes of any type other than ELEMENT_NODE and ATTRIBUTE_NODE and nodes created with a DOM Level 1 method, such as Document.createElement(), this is always null.

Note: Per the Namespaces in XML Specification [XML Namespaces] an attribute does not inherit its namespace from the element it is attached to. If an attribute is not explicitly given a namespace, it simply has no namespace.

@since
DOM Level 2
The node immediately following this node. If there is no such node, this returns null.
The name of this node, depending on its type; see the table above.
A code representing the type of the underlying object, as defined above.
The value of this node, depending on its type; see the table above. When it is defined to be null, setting it has no effect, including if the node is read-only.
Throws
DOMException DOMSTRING_SIZE_ERR: Raised when it would return more characters than fit in a DOMString variable on the implementation platform.
The Document object associated with this node. This is also the Document object used to create new nodes. When this node is a Document or a DocumentType which is not used with any Document yet, this is null.
@version
DOM Level 2
The Element node this attribute is attached to or null if this attribute is not in use.
@since
DOM Level 2
The parent of this node. All nodes, except Attr, Document, DocumentFragment, Entity, and Notation may have a parent. However, if a node has just been created and not yet added to the tree, or if it has been removed from the tree, this is null.
The namespace prefix of this node, or null if it is unspecified. When it is defined to be null, setting it has no effect, including if the node is read-only.
Note that setting this attribute, when permitted, changes the nodeName attribute, which holds the qualified name, as well as the tagName and name attributes of the Element and Attr interfaces, when applicable.
Setting the prefix to null makes it unspecified, setting it to an empty string is implementation dependent.
Note also that changing the prefix of an attribute that is known to have a default value, does not make a new attribute with the default value and the original prefix appear, since the namespaceURI and localName do not change.
For nodes of any type other than ELEMENT_NODE and ATTRIBUTE_NODE and nodes created with a DOM Level 1 method, such as createElement from the Document interface, this is always null.
@since
DOM Level 2
The node immediately preceding this node. If there is no such node, this returns null.
The type information associated with this attribute. While the type information contained in this attribute is guarantee to be correct after loading the document or invoking Document.normalizeDocument(), schemaTypeInfo may not be reliable if the node was moved.
@since
DOM Level 3
True if this attribute was explicitly given a value in the instance document, false otherwise. If the application changed the value of this attribute node (even if it ends up having the same value as the default value) then it is set to true. The implementation may handle attributes with default values from other schemas similarly but applications should use Document.normalizeDocument() to guarantee this information is up-to-date.
This attribute returns the text content of this node and its descendants. When it is defined to be null, setting it has no effect. On setting, any possible children this node may have are removed and, if it the new string is not empty or null, replaced by a single Text node containing the string this attribute is set to.
On getting, no serialization is performed, the returned string does not contain any markup. No whitespace normalization is performed and the returned string does not contain the white spaces in element content (see the attribute Text.isElementContentWhitespace). Similarly, on setting, no parsing is performed either, the input string is taken as pure textual content.
The string returned is made of the text content of this node depending on its type, as defined below:
Node type Content
ELEMENT_NODE, ATTRIBUTE_NODE, ENTITY_NODE, ENTITY_REFERENCE_NODE, DOCUMENT_FRAGMENT_NODE concatenation of the textContent attribute value of every child node, excluding COMMENT_NODE and PROCESSING_INSTRUCTION_NODE nodes. This is the empty string if the node has no children.
TEXT_NODE, CDATA_SECTION_NODE, COMMENT_NODE, PROCESSING_INSTRUCTION_NODE nodeValue
DOCUMENT_NODE, DOCUMENT_TYPE_NODE, NOTATION_NODE null
Throws
DOMException DOMSTRING_SIZE_ERR: Raised when it would return more characters than fit in a DOMString variable on the implementation platform.
@since
DOM Level 3
Retrieves the object associated to a key on a this node. The object must first have been set to this node by calling setUserData with the same key.
Parameters
keyThe key the object is associated to.
Return
Returns the DOMUserData associated to the given key on this node, or null if there was none.
@since
DOM Level 3
On retrieval, the value of the attribute is returned as a string. Character and general entity references are replaced with their values. See also the method getAttribute on the Element interface.
On setting, this creates a Text node with the unparsed contents of the string, i.e. any characters that an XML processor would recognize as markup are instead treated as literal text. See also the method Element.setAttribute().
Some specialized implementations, such as some [SVG 1.1] implementations, may do normalization automatically, even after mutation; in such case, the value on retrieval may differ from the value on setting.
Returns whether this node (if it is an element) has any attributes.
Return
Returns true if this node has any attributes, false otherwise.
@since
DOM Level 2
Returns whether this node has any children.
Return
Returns true if this node has any children, false otherwise.
Inserts the node newChild before the existing child node refChild. If refChild is null, insert newChild at the end of the list of children.
If newChild is a DocumentFragment object, all of its children are inserted, in the same order, before refChild. If the newChild is already in the tree, it is first removed.

Note: Inserting a node before itself is implementation dependent.

Parameters
newChildThe node to insert.
refChildThe reference node, i.e., the node before which the new node must be inserted.
Return
The node being inserted.
Throws
DOMException HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the newChild node, or if the node to insert is one of this node's ancestors or this node itself, or if this node is of type Document and the DOM application attempts to insert a second DocumentType or Element node.
WRONG_DOCUMENT_ERR: Raised if newChild was created from a different document than the one that created this node.
NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly or if the parent of the node being inserted is readonly.
NOT_FOUND_ERR: Raised if refChild is not a child of this node.
NOT_SUPPORTED_ERR: if this node is of type Document, this exception might be raised if the DOM implementation doesn't support the insertion of a DocumentType or Element node.
@version
DOM Level 3
This method checks if the specified namespaceURI is the default namespace or not.
Parameters
namespaceURIThe namespace URI to look for.
Return
Returns true if the specified namespaceURI is the default namespace, false otherwise.
@since
DOM Level 3
Tests whether two nodes are equal.
This method tests for equality of nodes, not sameness (i.e., whether the two nodes are references to the same object) which can be tested with Node.isSameNode(). All nodes that are the same will also be equal, though the reverse may not be true.
Two nodes are equal if and only if the following conditions are satisfied:
  • The two nodes are of the same type.
  • The following string attributes are equal: nodeName, localName, namespaceURI, prefix, nodeValue . This is: they are both null, or they have the same length and are character for character identical.
  • The attributes NamedNodeMaps are equal. This is: they are both null, or they have the same length and for each node that exists in one map there is a node that exists in the other map and is equal, although not necessarily at the same index.
  • The childNodes NodeLists are equal. This is: they are both null, or they have the same length and contain equal nodes at the same index. Note that normalization can affect equality; to avoid this, nodes should be normalized before being compared.

For two DocumentType nodes to be equal, the following conditions must also be satisfied:
  • The following string attributes are equal: publicId, systemId, internalSubset.
  • The entities NamedNodeMaps are equal.
  • The notations NamedNodeMaps are equal.

On the other hand, the following do not affect equality: the ownerDocument, baseURI, and parentNode attributes, the specified attribute for Attr nodes, the schemaTypeInfo attribute for Attr and Element nodes, the Text.isElementContentWhitespace attribute for Text nodes, as well as any user data or event listeners registered on the nodes.

Note: As a general rule, anything not mentioned in the description above is not significant in consideration of equality checking. Note that future versions of this specification may take into account more attributes and implementations conform to this specification are expected to be updated accordingly.

Parameters
argThe node to compare equality with.
Return
Returns true if the nodes are equal, false otherwise.
@since
DOM Level 3
Returns whether this attribute is known to be of type ID (i.e. to contain an identifier for its owner element) or not. When it is and its value is unique, the ownerElement of this attribute can be retrieved using the method Document.getElementById . The implementation could use several ways to determine if an attribute node is known to contain an identifier:
  • If validation occurred using an XML Schema [XML Schema Part 1] while loading the document or while invoking Document.normalizeDocument(), the post-schema-validation infoset contributions (PSVI contributions) values are used to determine if this attribute is a schema-determined ID attribute using the schema-determined ID definition in [XPointer] .
  • If validation occurred using a DTD while loading the document or while invoking Document.normalizeDocument(), the infoset [type definition] value is used to determine if this attribute is a DTD-determined ID attribute using the DTD-determined ID definition in [XPointer] .
  • from the use of the methods Element.setIdAttribute(), Element.setIdAttributeNS(), or Element.setIdAttributeNode(), i.e. it is an user-determined ID attribute;

    Note: XPointer framework (see section 3.2 in [XPointer] ) consider the DOM user-determined ID attribute as being part of the XPointer externally-determined ID definition.

  • using mechanisms that are outside the scope of this specification, it is then an externally-determined ID attribute. This includes using schema languages different from XML schema and DTD.

If validation occurred while invoking Document.normalizeDocument(), all user-determined ID attributes are reset and all attribute nodes ID information are then reevaluated in accordance to the schema used. As a consequence, if the Attr.schemaTypeInfo attribute contains an ID type, isId will always return true.
@since
DOM Level 3
Returns whether this node is the same node as the given one.
This method provides a way to determine whether two Node references returned by the implementation reference the same object. When two Node references are references to the same object, even if through a proxy, the references may be used completely interchangeably, such that all attributes have the same values and calling the same DOM method on either reference always has exactly the same effect.
Parameters
otherThe node to test against.
Return
Returns true if the nodes are the same, false otherwise.
@since
DOM Level 3
Tests whether the DOM implementation implements a specific feature and that feature is supported by this node, as specified in .
Parameters
featureThe name of the feature to test.
versionThis is the version number of the feature to test.
Return
Returns true if the specified feature is supported on this node, false otherwise.
@since
DOM Level 2
Look up the namespace URI associated to the given prefix, starting from this node.
See for details on the algorithm used by this method.
Parameters
prefixThe prefix to look for. If this parameter is null, the method will return the default namespace URI if any.
Return
Returns the associated namespace URI or null if none is found.
@since
DOM Level 3
Look up the prefix associated to the given namespace URI, starting from this node. The default namespace declarations are ignored by this method.
See for details on the algorithm used by this method.
Parameters
namespaceURIThe namespace URI to look for.
Return
Returns an associated namespace prefix if found or null if none is found. If more than one prefix are associated to the namespace prefix, the returned namespace prefix is implementation dependent.
@since
DOM Level 3
Puts all Text nodes in the full depth of the sub-tree underneath this Node, including attribute nodes, into a "normal" form where only structure (e.g., elements, comments, processing instructions, CDATA sections, and entity references) separates Text nodes, i.e., there are neither adjacent Text nodes nor empty Text nodes. This can be used to ensure that the DOM view of a document is the same as if it were saved and re-loaded, and is useful when operations (such as XPointer [XPointer] lookups) that depend on a particular document tree structure are to be used. If the parameter "normalize-characters" of the DOMConfiguration object attached to the Node.ownerDocument is true, this method will also fully normalize the characters of the Text nodes.

Note: In cases where the document contains CDATASections, the normalize operation alone may not be sufficient, since XPointers do not differentiate between Text nodes and CDATASection nodes.

@version
DOM Level 3
Removes the child node indicated by oldChild from the list of children, and returns it.
Parameters
oldChildThe node being removed.
Return
The node removed.
Throws
DOMException NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.
NOT_FOUND_ERR: Raised if oldChild is not a child of this node.
NOT_SUPPORTED_ERR: if this node is of type Document, this exception might be raised if the DOM implementation doesn't support the removal of the DocumentType child or the Element child.
@version
DOM Level 3
Replaces the child node oldChild with newChild in the list of children, and returns the oldChild node.
If newChild is a DocumentFragment object, oldChild is replaced by all of the DocumentFragment children, which are inserted in the same order. If the newChild is already in the tree, it is first removed.

Note: Replacing a node with itself is implementation dependent.

Parameters
newChildThe new node to put in the child list.
oldChildThe node being replaced in the list.
Return
The node replaced.
Throws
DOMException HIERARCHY_REQUEST_ERR: Raised if this node is of a type that does not allow children of the type of the newChild node, or if the node to put in is one of this node's ancestors or this node itself, or if this node is of type Document and the result of the replacement operation would add a second DocumentType or Element on the Document node.
WRONG_DOCUMENT_ERR: Raised if newChild was created from a different document than the one that created this node.
NO_MODIFICATION_ALLOWED_ERR: Raised if this node or the parent of the new node is readonly.
NOT_FOUND_ERR: Raised if oldChild is not a child of this node.
NOT_SUPPORTED_ERR: if this node is of type Document, this exception might be raised if the DOM implementation doesn't support the replacement of the DocumentType child or Element child.
@version
DOM Level 3
The value of this node, depending on its type; see the table above. When it is defined to be null, setting it has no effect, including if the node is read-only.
Throws
DOMException NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly and if it is not defined to be null.
The namespace prefix of this node, or null if it is unspecified. When it is defined to be null, setting it has no effect, including if the node is read-only.
Note that setting this attribute, when permitted, changes the nodeName attribute, which holds the qualified name, as well as the tagName and name attributes of the Element and Attr interfaces, when applicable.
Setting the prefix to null makes it unspecified, setting it to an empty string is implementation dependent.
Note also that changing the prefix of an attribute that is known to have a default value, does not make a new attribute with the default value and the original prefix appear, since the namespaceURI and localName do not change.
For nodes of any type other than ELEMENT_NODE and ATTRIBUTE_NODE and nodes created with a DOM Level 1 method, such as createElement from the Document interface, this is always null.
Throws
DOMException INVALID_CHARACTER_ERR: Raised if the specified prefix contains an illegal character according to the XML version in use specified in the Document.xmlVersion attribute.
NO_MODIFICATION_ALLOWED_ERR: Raised if this node is readonly.
NAMESPACE_ERR: Raised if the specified prefix is malformed per the Namespaces in XML specification, if the namespaceURI of this node is null, if the specified prefix is "xml" and the namespaceURI of this node is different from " http://www.w3.org/XML/1998/namespace", if this node is an attribute and the specified prefix is "xmlns" and the namespaceURI of this node is different from "http://www.w3.org/2000/xmlns/", or if this node is an attribute and the qualifiedName of this node is "xmlns" [XML Namespaces] .
@since
DOM Level 2
This attribute returns the text content of this node and its descendants. When it is defined to be null, setting it has no effect. On setting, any possible children this node may have are removed and, if it the new string is not empty or null, replaced by a single Text node containing the string this attribute is set to.
On getting, no serialization is performed, the returned string does not contain any markup. No whitespace normalization is performed and the returned string does not contain the white spaces in element content (see the attribute Text.isElementContentWhitespace). Similarly, on setting, no parsing is performed either, the input string is taken as pure textual content.
The string returned is made of the text content of this node depending on its type, as defined below:
Node type Content
ELEMENT_NODE, ATTRIBUTE_NODE, ENTITY_NODE, ENTITY_REFERENCE_NODE, DOCUMENT_FRAGMENT_NODE concatenation of the textContent attribute value of every child node, excluding COMMENT_NODE and PROCESSING_INSTRUCTION_NODE nodes. This is the empty string if the node has no children.
TEXT_NODE, CDATA_SECTION_NODE, COMMENT_NODE, PROCESSING_INSTRUCTION_NODE nodeValue
DOCUMENT_NODE, DOCUMENT_TYPE_NODE, NOTATION_NODE null
Throws
DOMException NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.
@since
DOM Level 3
Associate an object to a key on this node. The object can later be retrieved from this node by calling getUserData with the same key.
Parameters
keyThe key to associate the object to.
dataThe object to associate to the given key, or null to remove any existing association to that key.
handlerThe handler to associate to that key, or null.
Return
Returns the DOMUserData previously associated to the given key on this node, or null if there was none.
@since
DOM Level 3
On retrieval, the value of the attribute is returned as a string. Character and general entity references are replaced with their values. See also the method getAttribute on the Element interface.
On setting, this creates a Text node with the unparsed contents of the string, i.e. any characters that an XML processor would recognize as markup are instead treated as literal text. See also the method Element.setAttribute().
Some specialized implementations, such as some [SVG 1.1] implementations, may do normalization automatically, even after mutation; in such case, the value on retrieval may differ from the value on setting.
Throws
DOMException NO_MODIFICATION_ALLOWED_ERR: Raised when the node is readonly.