Untitled

<head>
<script type="text/javascript">
function popup()
{
confirm ("Welcome!");
}
</script>
</head>

<body>
 <button onclick="popup()">Try it</button>
 </body>

<head>
<script type="text/javascript">
function popup()
{
document.getElementById("div").innerHTML="Welcome!"
}
</script>
</head>
<body>
 <button onclick="popup()">Try it</button>
 <div id="div"></div>
 </body>

<html>
    <head>
        <script src="https://code.jquery.com/jquery-2.1.0.min.js"></script>
        <script>
            jQuery(document).ready(function() {
                jQuery('#mybutton').click(function() {
                    jQuery('#mytext').append('This is a line of text');
                });
            });
       </script>
    </head>
    <body>
         <button id="mybutton">Try it</button>
            <div id="mytext"></div>
    </body>
</html>