JavaScript (abbreviated to JS) is a programming language used on web pages. The particularity of JavaScript is that it is activated on the client side. That is to say that it is your computer that will execute the JS code via the web browser (unlike the PHP which is executed by the server).
JavaScript is used to bring additional functionality to web pages, including interactivity to a site. For example, if your theme uses a slider (also called carousel, see the definition here), chances are it’s using JavaScript to make it work.
Here are other examples of what you can do with JavaScript in a web page:
- Open pop-ups;
- Scroll through content;
- Insert a dynamic menu that expands as the mouse passes over it;
- Display a date selector;
- Display a progress bar.
Be careful not to confuse JavaScript with Java, which is another computer language.