What is the HTML DOM?

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The HTML DOM is an Object Model for HTML. It defines:

HTML elements as objects
Properties for all HTML elements
Methods for all HTML elements
Events for all HTML elements

The HTML DOM is an API (Programming Interface) for JavaScript:

JavaScript can add/change/remove HTML elements
JavaScript can add/change/remove HTML attributes
JavaScript can add/change/remove CSS styles
JavaScript can react to HTML events
JavaScript can add/change/remove HTML events

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

Finding HTML Elements

When you want to access HTML elements with JavaScript, 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 CSS selectors
Finding HTML elements by HTML object collections

Finding HTML Element by Id

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

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

Example

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

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

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

Finding HTML Elements by Tag Name

This example finds all <p> elements:

Example

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

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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");

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Finding HTML Elements by Class Name

If you want to find all HTML elements with the same class name, use getElementsByClassName().

This example returns a list of all elements with class="intro".

Example

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

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Finding elements by class name does not work in Internet Explorer 8 and earlier versions.

Finding HTML Elements by CSS Selectors

If you want to find all HTML elements that matches a specified CSS selector (id, class names, types, attributes, values of attributes, etc), use the querySelectorAll() method.

This example returns a list of all <p> elements with class="intro".

Example

var x = document.querySelectorAll("p.intro");

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The querySelectorAll() method does not work in Internet Explorer 8 and earlier versions.

Finding HTML Elements by HTML Object Collections

HTML object collections are also accessible:

HTML DOM Tutorial

Full HTMLDOM Tutorial

This has been a short introduction to HTMLDOM.

For a full HTMLDOM tutorial go to W3Schools HTMLDOM Tutorial.

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