JavaScript HTML DOM Nodelist

A nodelist is an array of nodes (like an array of all HTML elements)

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HTML DOM Node List

The getElementsByTagName() method returns a node list. A node list is an array of nodes.

The following code selects all <p> nodes in a document:

Example

var x=document.getElementsByTagName("p");

The nodes can be accessed by index number. To access the second <p> you can write:

y=x[1];

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Note: The index starts at 0.

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HTML DOM Node List Length

The length property defines the number of nodes in a node-list.

You can loop through a node-list by using the length property:

Example

x=document.getElementsByTagName("p");

for (i=0;i<x.length;i++)
{
document.write(x[i].innerHTML);
document.write("<br />");
}

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Example explained:

1. Get all <p> element nodes
2. For each <p> element, output the value of its text node

JavaScript HTML DOM Elements (Nodes)

Adding and Removing Nodes (HTML Elements)

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Creating New HTML Elements (Nodes)

To add a new element to the HTML DOM, you must create the element (element node) first, and then append it to an existing element.

 Example

<div id="div1">
<p id="p1">This is a paragraph.</p>
<p id="p2">This is another paragraph.</p>
</div>

<script>
var para=document.createElement("p");
var node=document.createTextNode("This is new.");
para.appendChild(node);

var element=document.getElementById("div1");
element.appendChild(para);
</script>

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Example Explained 

This code creates a new <p> element:

var para=document.createElement("p");

To add text to the <p> element, you must create a text node first. This code creates a text node:

var node=document.createTextNode("This is a new paragraph.");

Then you must append the text node to the <p> element:

para.appendChild(node);

Finally you must append the new element to an existing element.

This code finds an existing element:

var element=document.getElementById("div1");

This code appends the new element to the existing element:

element.appendChild(para);

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Creating new HTML Elements - insertBefore()

The appendChild() method in the previous example, appended the new element as the last child of the parent.

If you don't want that you can use the insertBefore() method:

 Example

<div id="div1">
<p id="p1">This is a paragraph.</p>
<p id="p2">This is another paragraph.</p>
</div>

<script>
var para=document.createElement("p");
var node=document.createTextNode("This is new.");
para.appendChild(node);

var element=document.getElementById("div1");
var child=document.getElementById("p1");
element.insertBefore(para,child);
</script>

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Removing Existing HTML Elements

To remove an HTML element, you must know the parent of the element:

Example

<div id="div1">
<p id="p1">This is a paragraph.</p>
<p id="p2">This is another paragraph.</p>
</div>

<script>
var parent=document.getElementById("div1");
var child=document.getElementById("p1");
parent.removeChild(child);
</script>

Try it Yourself »

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Example Explained 

This HTML document contains a <div> element with two child nodes (two <p> elements):

<div id="div1">
<p id="p1">This is a paragraph.</p>
<p id="p2">This is another paragraph.</p>
</div>

Find the element with id="div1":

var parent=document.getElementById("div1");

Find the <p> element with id="p1":

var child=document.getElementById("p1");

Remove the child from the parent:

parent.removeChild(child);

	It would be nice to be able to remove an element without referring to the parent. But sorry. The DOM needs to know both the element you want to remove, and its parent.

Here is a common workaround: Find the child you want to remove, and use its parentNode property to find the parent:

var child=document.getElementById("p1");
child.parentNode.removeChild(child);

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Replacing HTML Elements 

To replace an element to the HTML DOM, use the replaceChild() method:

Example

<div id="div1">
<p id="p1">This is a paragraph.</p>
<p id="p2">This is another paragraph.</p>
</div>

<script>
var para=document.createElement("p");
var node=document.createTextNode("This is new.");
para.appendChild(node);

var parent=document.getElementById("div1");
var child=document.getElementById("p1");
parent.replaceChild(para,child);
</script>

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JavaScript HTML DOM Events

HTML DOM allows JavaScript to react to HTML events.

Example

Mouse Over Me

Click Me

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Reacting to Events

A JavaScript can be executed when an event occurs, like when a user clicks on an HTML element.

To execute code when a user clicks on an element, add JavaScript code to an HTML event attribute:

onclick=JavaScript

Examples of HTML events:

• When a user clicks the mouse
• When a web page has loaded
• When an image has been loaded
• When the mouse moves over an element
• When an input field is changed
• When an HTML form is submitted
• When a user strokes a key

In this example, the content of the <h1> element is changed when a user clicks on it:

Example

<!DOCTYPE html>
<html>
<body>
<h1 onclick="this.innerHTML='Ooops!'">Click on this text!</h1>
</body>
</html>

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In this example, a function is called from the event handler:

Example

<!DOCTYPE html>
<html>
<head>
<script>
function changetext(id)
{
id.innerHTML="Ooops!";
}
</script>
</head>
<body>
<h1 onclick="changetext(this)">Click on this text!</h1>
</body>
</html>

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HTML Event Attributes

To assign events to HTML elements you can use event attributes.

Example

Assign an onclick event to a button element:

<button onclick="displayDate()">Try it</button>

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In the example above, a function named displayDate will be executed when the button is clicked.

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Assign Events Using the HTML DOM

The HTML DOM allows you to assign events to HTML elements using JavaScript:

Example

Assign an onclick event to a button element:

<script>
document.getElementById("myBtn").onclick=function(){displayDate()};
</script>

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In the example above, a function named displayDate is assigned to an HTML element with the id="myBtn".

The function will be executed when the button is clicked.

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The onload and onunload Events

The onload and onunload events are triggered when the user enters or leaves the page.

The onload event can be used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.

The onload and onunload events can be used to deal with cookies.

Example

<body onload="checkCookies()">

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The onchange Event

The onchange event are often used in combination with validation of input fields.

Below is an example of how to use the onchange. The upperCase() function will be called when a user changes the content of an input field.

Example

<input type="text" id="fname" onchange="upperCase()">

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The onmouseover and onmouseout Events

The onmouseover and onmouseout events can be used to trigger a function when the user mouses over, or out of, an HTML element.

Example

A simple onmouseover-onmouseout example:

Mouse Over Me

Try it Yourself »

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The onmousedown, onmouseup and onclick Events

The onmousedown, onmouseup, and onclick events are all parts of a mouse-click. First when a mouse-button is clicked, the onmousedown event is triggered, then, when the mouse-button is released, the onmouseup event is triggered, finally, when the mouse-click is completed, the onclick event is triggered.

Example

A simple onmousedown-onmouseup example:

Click Me

Try it Yourself »

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More Examples

onmousedown and onmouseup
Change an image when a user holds down the mouse button.

onload
Display an alert box when the page has finished loading.

onfocus
Change the background-color of an input field when it gets focus.

Mouse Events
Change the color of an element when the cursor moves over it.

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HTML DOM Event Object Reference

For a list of all HTML DOM events, look at our complete HTML DOM Event Object Reference.

JavaScript HTML DOM

With the HTML DOM, JavaScript can access and change all the elements of an HTML document.

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The HTML DOM (Document Object Model)

When a web page is loaded, the browser creates a Document Object Model of the page.

The HTML DOM model is constructed as a tree of Objects:

The HTML DOM Tree of Objects

With the object model, JavaScript gets all the power it needs to create dynamic HTML:

• JavaScript can change all the HTML elements in the page
• JavaScript can change all the HTML attributes in the page
• JavaScript can change all the CSS styles in the page
• JavaScript can remove existing HTML elements and attributes
• JavaScript can add new HTML elements and attributes
• JavaScript can react to all existing HTML events in the page
• JavaScript can create new HTML events in the page

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What You Will Learn

In the next chapters of this tutorial you will learn:

• How to change the content of HTML elements
• How to change the style (CSS) of HTML elements
• How to react to HTML DOM events
• How to add and delete HTML elements

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What is the DOM?

The DOM is a W3C (World Wide Web Consortium) standard.

The DOM defines a standard for accessing documents:

"The W3C Document Object Model (DOM) is a platform and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document."

The W3C DOM standard is separated into 3 different parts:

• Core DOM - standard model for all document types
• XML DOM - standard model for XML documents
• HTML DOM - standard model for HTML documents

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What is the HTML DOM?

The HTML DOM is a standard object model and programming interface for HTML. It defines:

• The HTML elements as objects
• The properties of all HTML elements
• The methods to access all HTML elements
• The events for all HTML elements

In other words: The HTML DOM is a standard for how to get, change, add, or delete HTML elements.