JavaScript can put dynamic text into an HTML page --
A JavaScript statement like this: document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page
JavaScript can react to events -
A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
JavaScript can be used to validate data -
A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing.
JavaScript can be used to detect the visitor's browser --
A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
JavaScript can be used to create cookies- -
A JavaScript can be used to store and retrieve information on the visitor's computer