HTML and JavaScript
JavaScript - Introduced in 1995 - Object-oriented programming (OOP) - Allows interaction with the HTML elements
In the next example the text change to green after clicking the text.
<!DOCTYPE HTML>
<html lang="en">
<head>
<style type="text/css">
p {
color: red;
}
</style>
<script language="javascript">
// displays an alert
alert('Click on the Hello World text!');
// change text color
function changeColor(color){
document.getElementById('hello').style.color = color;
}
</script>
<title>A title</title>
</head>
<body>
<!-- onclick attributes applies the JavaScript
function changeColor define above -->
<p id="hello" onclick="changeColor('green')">Hello World</p>
</body>
</html>