DOM Navigation

With the HTML DOM, you can navigate or move the node tree using node relationships.


DOM Nodes

According to the W3C HTML DOM standard, everything in an HTML document is a node:

  • The entire document is a document node
  • Every HTML element is an element node
  • The text inside HTML elements are text nodes
  • Every HTML attribute is an attribute node (deprecated)
  • All comments are comment nodes

With the HTML DOM, all nodes in the node tree can be accessed or controlled by JavaScript.

New nodes can be created, and all nodes can be modified or deleted.


Node Relationships

The nodes in the node tree have a hierarchical(parent-child) relationship to each other.

The terms parent, child, and sibling are used to describe the relationships.

  • In a node tree, the top node is called the root (or root node)
    • Every node has exactly one parent, except the root (which has no parent)
    • A node can have a number or multiple of children
    • Siblings (brothers or sisters) are nodes with the same parent.
<html>
  <head>
    <title>This is DOM Tutorial</title>
  </head>

  <body>
    <h1>DOM Lesson 1</h1>
    <p>My world!</p>
  </body>
</html>

From the HTML above you can read:<html> is the root node

  • <html> has no parents
  • <html> is the parent of <head> and <body>
  • <head> is the first child of <html>
  • <body> is the last child of <html>

and:

  • <head> has one child: <title>
  • <title> has one child (a text node): “DOM Tutorial”
  • <body> has two children: <h1> and <p>
  • <h1> has one child: “DOM Lesson one”
  • <p> has one child: “Hello world!”
  • <h1> and <p> are siblings

Navigating Between Nodes

You can use the below node properties to navigate between nodes with JavaScript:

  1. parentNode
  2. childNodes[nodenumber]
  3. firstChild
  4. lastChild
  5. nextSibling
  6. previousSibling

Child Nodes and Node Values

     Note:- A common error in DOM processing is to expect that an element node can contain text.

Example:-
<title id="title">This is DOM Tutorial</title> 

The element node <title> (in the example above) does not contain text.

It contains a text node with the value “This is DOM Tutorial”.

The value of the text node can be controlled by the node’s innerHTML property:

var myTitle = document.getElementById("title").innerHTML;

Accessing the innerHTML property is the same as accessing the nodeValue of the first child:

var myTitle = document.getElementById("title").firstChild.nodeValue;

Accessing the first child can also be done like this:

var myTitle = document.getElementById("title").childNodes[0].nodeValue;

All of above 3 following examples get the text of an <span> element and copies it into a <h1> element:

Input:-
<!DOCTYPE html>
<html>
<body>

<span id="span1">My Page</span>
<h1 id="h1"></h1>

<script>
document.getElementById("h1").innerHTML = document.getElementById("span1").innerHTML;
</script>

</body>
</html> 

Output :-

Input:-
<!DOCTYPE html>
<html>
<body>

<span id="span1">My Page</span>
<h1 id="h1"></h1>

<script>
document.getElementById("h1").innerHTML = document.getElementById("span1").firstChild.nodeValue;
</script>

</body>
</html>

Output :-

Input:-
<!DOCTYPE html>
<html>
<body>

<span id="span1">My Page</span>
<h1 id="h1"></h1>

<script>
document.getElementById("h1").innerHTML = document.getElementById("span1").childNodes[0].nodeValue;
</script>

</body>
</html>

Output :-


InnerHTML

In this we use the innerHTML property to retrieve or get the content of an HTML element.

However, above methods are useful for understanding the tree structure and the navigation of the DOM.


DOM Root Nodes

There are two special properties that allow user to access full document:

  • document.body – The body of the document
  • document.documentElement – The full document
Input:-
<html>
<body>

<p>My World!</p>
<div>
<p>This is DOM World!</p>
<p>This example access the <b>document.body</b> property.</p>
</div>

<script>
alert(document.body.innerHTML);
</script>

</body>
</html>

Output :-


nodeName Property

The nodeName property gives the name of a node.

  • nodeName is read-only
  • nodeName of an element node that is the same as the tag name
  • nodeName of an attribute node that is the attribute name
  • nodeName of a text node that is always #text
  • nodeName of the document node that is always #document
Input:-
<!DOCTYPE html>
<html>
<body>

<span id="span1">My Page</span>
<h1 id="h1"></h1>

<script>
document.getElementById("h1").innerHTML = document.getElementById("span1").nodeName;
</script>

</body>
</html>

Output :-

Note:- nodeName property always contains the uppercase tag name of an HTML element.


nodeValue Property

The nodeValue property gives the value of a node.

  • nodeValue for element nodes is null
  • nodeValue for text nodes that is the text itself
  • nodeValue for attribute nodes that is the attribute value

nodeType Property

The nodeType property is read only mode. It returns the type of a node.

Input:-
<!DOCTYPE html>
<html>
<body>

<span id="span1">My Page</span>
<h1 id="h1"></h1>

<script>
document.getElementById("h1").innerHTML = document.getElementById("span1").nodeType;
</script>

</body>
</html>

Output :-

The most important nodeType properties are:

NodeTypeExample
ELEMENT_NODE1<h1 class=”heading”>lecturely</h1>
ATTRIBUTE_NODE2 class = “heading” (deprecated)
TEXT_NODE3lecturely
COMMENT_NODE8<!– This is a comment –>
DOCUMENT_NODE9The HTML document itself (the parent of <html>)
DOCUMENT_TYPE_NODE10<!Doctype html>