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JavaScript HTML DOM

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

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

DOM HTML tree

With a programmable 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 react to all the events in the page

Finding HTML Elements

Often, with JavaScript, you want to manipulate HTML elements.

To do so, you have to find the elements first. There are a couple of ways to do this:

  • Finding HTML elements by id
  • Finding HTML elements by tag name
  • Finding HTML elements by class name

Finding HTML Elements by Id

The easiest way to find HTML elements in the DOM, is by using the element id.

This example finds the element with id="intro":

Example

var x=document.getElementById("intro");

Try it yourself »

If the element is found, the method will return the element as an object (in x).

If the element is not found, x will contain null.

Finding HTML Elements by Tag Name

This example finds the element with id="main", and then finds all <p> elements inside "main":

Example

var x=document.getElementById("main");
var y=x.getElementsByTagName("p");

Try it yourself »

lamp Finding elements by class name does not work in Internet Explorer 5,6,7, and 8.

HTML DOM Tutorial

In the next chapters of this tutorial you will learn:

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

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