fix (PostMessage) Switch postMessage dispatch implementation between …

…web and mobile to get rid of duplicates

src/PostMessage.coffee

@@ -1,3 +1,5 @@
+isMobile = /AppGyver|Crosswalk/.test(navigator.userAgent)
+
 class PostMessage
 
   @originalPostMessage: do (win = window)->
@@ -10,20 +12,24 @@ class PostMessage
       catch e
         console.log "Could not pass postMessage to original window.postMessage: #{e}", args[0]
 
-  @postMessage: (message, targetOrigin) =>
-    escapedJSONMessage = escape(JSON.stringify(message))
-
-    steroids.nativeBridge.nativeCall
-      method: "broadcastJavascript"
-      parameters:
-        javascript: "steroids.PostMessage.dispatchMessageEvent('#{escapedJSONMessage}', '*');"
-      successCallbacks: []
-      failureCallbacks: []
-      recurringCallbacks: []
-
-    @originalPostMessage message, targetOrigin
-
-
+  # Switch between native and web implementations for postMessage dispatching.
+  # If we are in web, there's no native bridge to dispatch messages.
+  # If we are in mobile, we don't want to dispatch through window as well;
+  # we would get duplicate postMessage events in the originating window.
+  @postMessage: switch
+    when !isMobile
+      @originalPostMessage
+    else
+      (message, targetOrigin) =>
+        escapedJSONMessage = escape(JSON.stringify(message))
+
+        steroids.nativeBridge.nativeCall
+          method: "broadcastJavascript"
+          parameters:
+            javascript: "steroids.PostMessage.dispatchMessageEvent('#{escapedJSONMessage}', '*');"
+          successCallbacks: []
+          failureCallbacks: []
+          recurringCallbacks: []
 
   @dispatchMessageEvent: (escapedJSONMessage, targetOrigin) =>
     #wrap in a setTimeout to garantee that runs in the webkit thread.