In WebSocketTransport constructor, throw an exception if !WebSocket
diff --git a/js/WebSocketTransport.js b/js/WebSocketTransport.js
index eb8a938..bc2a3e7 100644
--- a/js/WebSocketTransport.js
+++ b/js/WebSocketTransport.js
@@ -4,6 +4,9 @@
  */
 
 var WebSocketTransport = function WebSocketTransport() {    
+    if (!WebSocket)
+        throw new Error("WebSocket support is not available on this platform.");
+    
 	this.ws = null;
     this.connectedHost = null; // Read by NDN.
     this.connectedPort = null; // Read by NDN.