Edit in JSFiddle

// main.js
(function () {
  //Creates the anonymous user agent so that you can send messages
  var userAgent = new SIP.UA();
  
  // send the message when the button is clicked
  document.getElementById('send').addEventListener("click", function() { 
    userAgent.message("bryan@wadearcade.onsip.com", "Hello Bryan!");}, false);
}) ();
<!DOCTYPE html>
<html>
  <body>
    <button id="send">Send Message</button> 

    <script src="sip-devel.min.js"></script> 
    <script src="main.js"></script> 
  </body>
</html>