constructor.html

<!doctype html>
<html>
<head>
	<script src="../polymer/polymer.js"></script>
</head>
<body>
	<polymer-element name="my-element" constructor="MyElement">
	  <template>
	    <h2>
	      Hello, I'm a Polymer element
	    </h2>
	  </template>
	  <script>
	    Polymer("my-element");
	  </script>
	</polymer-element>

	<my-element></my-element>

	<script>
	document.addEventListener('WebComponentsReady', function() {
	  console.log(window.MyElement);
	});
	</script>
</body>
</html>