Tryit Editor v1.7

Source Code:

Result:

<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("button").click(function(){
    $("p:first").addClass("intro note");
  });
});
</script>
<style type="text/css">
.intro
{
font-size:30px;
color:blue;
}
.note
{
background-color:yellow;
}
</style>
</head>
<body>

<h1>This is a heading</h1>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>

<button>Add two class names to the first p element</button>

</body>
</html>

Edit the code above and click "Submit Code" to see the result.

W3Schools.com - Try it yourself

Source Code:	Result:
<!DOCTYPE html> <html> <head> <script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"> </script> <script> $(document).ready(function(){ $("button").click(function(){ $("p:first").addClass("intro note"); }); }); </script> <style type="text/css"> .intro { font-size:30px; color:blue; } .note { background-color:yellow; } </style> </head> <body> <h1>This is a heading</h1> <p>This is a paragraph.</p> <p>This is another paragraph.</p> <button>Add two class names to the first p element</button> </body> </html>
Edit the code above and click "Submit Code" to see the result.	W3Schools.com - Try it yourself