professional_javascript_for_web/ch22/EventTargetExample01.htm

<!doctype html>
<html>
<head>
    <title>Event Target Example</title>
    <script type="text/javascript" src="EventTarget.js"></script>
</head>
<body>
    <div id="myDiv" style="background:red;"></div>

    <script type="text/javascript">
        
        function handleMessage(event){
            alert("Message received: " + event.message);
        }

        var target = new EventTarget();
        
        target.addHandler("message", handleMessage);

        target.fire({ type: "message", message: "Hello world!"});
        
        target.removeHandler("message", handleMessage);

        target.fire({ type: "message", message: "Hello world!"});


    </script>
</body>
</html>