DOM Navigation
DOM Navigation refers to the process of traversing and accessing different elements within the Document Object Model (DOM) hierarchy. It involves moving between parent and child nodes, sibling nodes, and finding specific elements based on various criteria.
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.
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:
- parentNode
- childNodes[nodenumber]
- firstChild
- lastChild
- nextSibling
- 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 the above 3 following examples get the text of an <span> element and copy it into an <h1> element:
Input:-
Output :-
Input:-
Output :-
Input:-
Output :-
InnerHTML
In this, we use the innerHTML property to retrieve or get the content of an HTML element.
However, the 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 users to access the full document:
- document.body - The body of the document
- document.documentElement - The full document
Input:-
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:-
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. It returns the type of a node.
Input:-
Output :-
The most important nodeType properties are:
|
Node |
Type |
Example |
|
ELEMENT_NODE |
1 |
<h1 class="heading">lecturely</h1> |
|
ATTRIBUTE_NODE |
2 |
class = "heading" (deprecated) |
|
TEXT_NODE |
3 |
lecturely |
|
COMMENT_NODE |
8 |
<!-- This is a comment --> |
|
DOCUMENT_NODE |
9 |
The HTML document itself (the parent of <html>) |
|
DOCUMENT_TYPE_NODE |
10 |
<!Doctype html> |
