DOM Interfaces
The document processing can be done two ways:
- Through generic Node interface.
- Specific interface defined for each nodeType.
Generic Node interface
The node of XML element has a minimum set of attributes and methods which can be used to manipulate tree structure. A generic Node interface can access other nodes through parent node, child node, siblings …etc relationship. It is root of all specific interfaces and is possible to access any object of the document.
Attributes defined in a Node interface are firstChild, lastChild, nextSibling, parentNode, and previousSibling.
Example attributes in Node interface
<book>
<title>Lamp is Lit</title>
<author>Ruskin Bond</author>
</book>
Where:
- First child of book is title.
- Parent Node of title is book.
- Last Child is author.
- Next Sibling of title is author.
- Previous Sibling of author is title.
Methods defined in Node interface are given below. A complete example of loading XML document and manipulating nodes are given at the end of the definitions. These code snippets can be placed at appropriate place in the code to get desired output.
insertBefore()
The insertBefore() method inserts new child node before specified child.
Syntax for insertBefore() method
xmldoc = loadXMLDoc(“myData.xml”);
newele = xmldoc.createElement(“newbooks”);
x = xmldoc.documentElement;
node = xmldoc.getElementsByTagName(“newbooks”)[3];
x.insertBefore(newele, node);
removeChild()
The removeChild() method removes a specific node from a document.
Syntax for removeChild() method
xmldoc = loadXMLDoc(“myData.xml”);
rem = xmldoc.getElementsByTagName(“newbooks”)[0];
xmldoc.document.removeChild(rem);
removeAttribute()
The removeAttribute() method removes specified attribute from document.
Syntax for removeAttribute() method
xmldoc = loadXMLDoc(“myData.xml”);
rem = xmldoc.getElementsByTagName(“newbooks”);
rem[0].removeAttribute(“cost”);
replaceChild()
The replaceChild() method replaces a specific child node from the document.
Syntax for replaceChild() method
xmldoc = loadXMLDoc(“myData.xml”);
newNode = xmldoc.createElement(“book”);
newName = xmldoc.createElement(“title”);
newText = xmldoc.createtextNode(“Fountain Pen”);
newName.appendChild(newText);
newNode.appendChild(newName);
createElement()
The createElement() method creates a new element node.
Syntax for createElement() method
xmldoc = loadXMLDoc(“myData.xml”);
newele = xmldoc.createElement(“newbooks”);
createAttribute()
The createAttribute() method creates a new attribute node.
Syntax for createAttribute() method
xmldoc = loadXMLDoc(“myData.xml”);
newatt = xmldoc.createAttribute(“edition”);
setAttribute()
The setAttribute() method sets attribute if it exists or creates new attribute if it does not exists.
Syntax for setAttribute() method
xmldoc = loadXMLDoc(“myData.xml”);
t = xmldoc.getElementsByTagName(“title”);
t[0].setAttribute(“cost”,”290”);
createTextNode()
The createTextNode() method creates a new text node.
Syntax for createTextNode() method
xmldoc = loadXMLDoc(“myData.xml”);
t = xmldoc.createElement(“title”);
thisText = xmldoc.createTextNode(“A day in front of Fire”);
t.appendChild(thisText);
x=xmlDoc.getElementByTagName(“book”)[2];
x.appendChild(t);
createCDATASection()
The createCDATASection() method creates a new CDATA section mode.
Syntax for createCDATASection() method
xmldoc = loadXMLDoc(“myData.xml”);
c = xmldoc.createCDATASection(“This book is sold > 7000 copies”);
x=xmlDoc.getElementByTagName(“book”)[2];
x.appendChild(c);
createComment()
The createComment() method creates a new comment node.
Syntax for createComment() method
xmldoc = loadXMLDoc(“myData.xml”);
c = xmldoc.createComment(“Best seller of this season”);
x=xmlDoc.getElementByTagName(“book”)[2];
x.appendChild(c);
Example with general node interface methods in XML
The XML file and Javascript file to load the XML.
myData.xml
<?xml version='1.0'?>
<root>
<data>
<text>
<author>P C Tejaswi</author>
<books>Karvaalo</books>
<award>State Academy</award>
</text>
<text>
<author>Kuvempu</author>
<books>Ramayana Darshanam</books>
<award>Gnanapeeta</award>
</text>
</data>
</root>
myData.html
<!DOCTYPE html>
<html>
<body>
<h3>DOM usage </h3>
<p id="para"> </p>
<script>
function loadFile(name){
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xhttp = new XMLHttpRequest();
}
else
{// code for IE6, IE5
xhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xhttp.open("GET",name,false);
xhttp.send();
return xhttp.responseXML;
}
xmldoc = loadFile("myData.xml");
document.write(xmldoc.documentElement.nodeName + " ");
document.write(xmldoc.getElementsByTagName("author")[0].childNodes[0].nodeValue + " ");
document.write(xmldoc.getElementsByTagName("book")[0].childNodes[0].nodeValue + " ");
document.write(xmldoc.getElementsByTagName("award")[0].childNodes[0].nodeValue + " ");
</script>
</body>
</html>
//output
DOM usage
root P C Tejaswi Karvaalo State Academy
Specific node interface
DOM level 1 has defined following specific interfaces to manipulate the XML document nodes:
Document
The Document interface refers to entire document.
DocumentFragment
The DocumentFragment interface represents fragment of XML document.
DocumentType
The DocumentType interface defines the DOCTYPE object.
EntityReference
The EntityReference interface represents the entity references of XML document.
Element
The Element interface refers to the element object of the XML document.
Attr
The Attr interface refers to the attribute of the Element object.
ProcessingInstruction
The ProcessingInstruction interface refers to the processing instructions in the document.
Comment
The Comment interface object represents content of comment in the document.
CDATASection
The CDATASection interface refers to CDATA section of the document.
Entity
The Entity interface represents parsed and unparsed data of XML.
Notation
The Notation interface is the non XML data in the XML document.
Node
The Node interface object represents single node in the document.
NodeList
The NodeList interface represents ordered list of nodes. The nodes can be accessed through index number starting from 0. The node automatically updates the element added, deleted from the list.
This interface has length method which returns the length of the node list.
This interface has item() method which returns the node at the specified index of the node list.
Syntax for NodeList interface
Xmldoc = loadxml(“myData.xml”);
X = xmldoc.getElementsByTagname(‘author’)
document.write(x.item(0).nodeName);
NamedNodeMap
The NamedNodeMap interface represents unordered list of nodes. The nodes can be returned in any particular order and can be accessed by any name.
length method
The length method has a length attribute which returns the number of nodes.
Example of length method
xmldoc = loadXMLDoc(“myData.xml”);
x = xmldoc.getElementsByTagName(“book”);
document.write(x.item(0).attributes.length);
getNamedItem()
The getNamedItem() method returns the node with given name.
Syntax for getNamedItem() method
namedNodeMap.getNamedItem(nodeName)
getNamedItemNS()
The getNamedItemNS() method returns a node with given name and namespace.
item()
The item() method returns node at given index.
Syntax for item() method
Node.item(index)
removeNamedIndex()
The removeNamedIndex() method removes the node with the given name.
Syntax for removeNamedIndex() method
namedNodeMap.removeNamedIndex(nodename)
removeNamedItemNS()
The removeNamedItemNS() method removes the node with given name and namespace.
setNamedItem()
The setNamedItem() method sets the name of given node.
setNamedItemNS()
The setNamedItemNS() method sets the name and namespace of the given node.
DOM Implementation
The DOM implementation has the list of methods which perform operations that are independent of any instance of DOM.The methods of DOM implementation are:
createDocument()
The createDocument() method returns a DOM Document object with specified type and doctype.
Syntax for createDocument() method
createDocument(namespaceURI, qualifiedName, doctype)
Where,
- namespaceURI – Namespace URI fo the document to be created.
- qualifiedName – Qualified name of the document to be created.
- doctype – Type of document to be created.
createDocumentType()
The createDocumentType() method creates an empty DocumentType node and returns it.
Syntax createDocumentType() method
createDocumentType(name, pubId, systemId)
Where,
- name is qualified name of the document type.
- pubId is external subset public identifier.
- systemId is external subset system identifier.
getFeature()
The getFeature() method returns an object which implements API’s of a specified feature and version.
Syntax getFeature() method
getFeature(feature, version)
Where,
- feature is name of the feature to test.
- version is the version number of the feature to test.
hasFeature()
The hasFeature() method tests if the DOM implementation has implemented a particular feature.
Syntax hasFeature() method
getFeature(feature,version)
Where,
- feature is name of the feature to test.
- version is the version number of the feature to test.
DOM Exception
DOM operations raise exceptions when an operation is impossible to perform because of logical reasons, data is lost, etc... The DOM methods return the error values when exception occurs.
List of DOM Exception ID’s, values and description is given below:
|
Error Name |
Error Code ID |
Description |
|---|---|---|
|
DOMException.INDEX_SIZE_ERR |
1 |
This error occurs if index is negative or greater than allowed value. |
|
DOMException.DOMSTRING_SIZE_ERR |
2 |
This error occurs if the range of text does not fit into the string. |
|
DOMException.HIERARCHY_REQUEST_ERR |
3 |
This error occurs if any Node is inserted somewhere it does n ot belong. |
|
DOMException.WRONG_DOCUMENT_ERR |
4 |
This error occurs if the node is used in another document than it was created. |
|
DOMException.INVALID_CHARACTER_ERR |
5 |
This error occurs if an invalid or illegal character is specified. |
|
DOMException.NO_DATA_ALLOWED_ERR |
6 |
This error occurs if the data specified for node is not allowed. |
|
DOMException.NO_MODIFICATION_ALLOWED_ERR |
7 |
This error occurs if the modification is attempted on an object where it is not allowed. |
|
DOMException.NOT_FOUND_ERR |
8 |
This error occurs if the node which does not exists is referenced |
|
DOMException.NOT_SUPPORTED_ERR |
9 |
This error occurs if the implementation does not support the requested type of object or operation. |
|
DOMException.INUSE_ATTRIBUTE_ERR |
10 |
This error occurs if the existing attribute is added to the document again. |
|
DOMException.INVALID_STATE_ERR |
11 |
This error occurs if the object that is no longer usable is attempted to use |
|
DOMException.SYNTAX_ERR |
12 |
This error occurs if an invalid or illegal string is specified. |
|
DOMException.INVALID_MODIFICATION_ERR |
13 |
This error occurs if the type of object is changed |
|
DOMException.NAMESPACE_ERR |
14 |
This error occurs if the objects are changed in a wrong way wrt namespaces. |
|
DOMException.INVALID_ACCESS_ERR |
15 |
This error occurs if the operation is not supported by the object. |
|
DOMException.VALIDATION_ERR |
16 |
This error occurs if validation error occurs after method such as insertBefore or removeChild is used. |
|
DOMException.MISMATCH_ERR |
17 |
This error occurs if type of element is incompatible with it’s expected type of the parameter associated. |
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