Javascript is the standard client-side scripting language used in website design. Javascript code runs within the browser on your pc or device when you view a website, and allows changes to be made dynamically, e.g. for animations or changes to what is displayed based upon user's settings such as screen sizes, etc.

Much of what Javascript has been used for in the past can now be done using CSS but scripting is still an essential tool for a website developer to be familiar with.