Using JavaScript

JavaScript is most commonly used for client-side scripting within an HTML document. As such, this section will focus on how to apply JavaScript in this way.

HTML provides a means of including JavaScript code in the form of the <script> element. Using the <script> element, JavaScript can be included in a web page in two ways:

• Internal Script
• External Script

Note: It is no longer necessary to include "type = text/javascript" within the <script> tag as JavaScript is the default scripting language in all modern browsers and in HTML5.

Internal Script

Internal scripts include JavaScript code directly in the markup by using the <script> tag, like this:

This method is a good choice for quickly testing a solution or adding code that is specific to a particular page.

External Script

External scripts instruct the browser to download a separate JavaScript file and execute it in the page. The src attribute points to the script file like any other URL.

The myscript.js file would look like this:

In most cases, this is the best solution for a few reasons:

• Placing the JavaScript code directly in the HTML file with an internal script makes the HTML files larger and harder to maintain.
• JavaScript can easily be included in multiple pages just by including the same <script> tag
• Most browsers cache JavaScript files so they don't have to download a script file twice when visiting another page that uses it.