Function in Javascript (Example)

<!DOCTYPE html>
<html>

<head>

<style>
#button1 {
height: 50px;
width: 76px;
background-color: blue;
color: yellow;
border: 3px solid green;
}
</style>

</head>

<body>

<h1 id="demo">This Text Is Going To Change After Someone Click The Lonely Button!</h1>

<button type ="button" id="button1" onclick="randomFunction()">Click me!</button>

<script>

function randomFunction()
{
   document.getElementById("demo").innerHTML = "THANK YOU, YOU CHANGED ME!";
}

</script>


</body>

</html>