Fixes #460

tool/input_sdk/lib/js/dart2js/js_dart2js.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Support for interoperating with JavaScript.
  *
  * This library provides access to JavaScript objects from Dart, allowing
  * Dart code to get and set properties, and call methods of JavaScript objects
  * and invoke JavaScript functions. The library takes care of converting
@@ skipping 102 matching lines @@
 
   /**
    * Constructs a new JavaScript object from [constructor] and returns a proxy
    * to it.
    */
   factory JsObject(JsFunction constructor, [List arguments]) {
     var ctor = constructor._jsObject;
     if (arguments == null) {
       return _wrapToDart(JS('', 'new #()', ctor));
     }
-    return _wrapToDart(JS('', 'new #(...#)', ctor, arguments));
+    var unwrapped = new List.from(arguments.map(_convertToJS));
+    return _wrapToDart(JS('', 'new #(...#)', ctor, unwrapped));
   }
 
   /**
    * Constructs a [JsObject] that proxies a native Dart object; _for expert use
    * only_.
    *
    * Use this constructor only if you wish to get access to JavaScript
    * properties attached to a browser host object, such as a Node or Blob, that
    * is normally automatically converted into a native Dart object.
    *
@@ skipping 415 matching lines @@
         '  for (let arg of arguments) {'
         '    args.push(arg);'
         '  }'
         '  return #(...args);'
         '}',
         f);
     _interopCaptureThisExpando[f] = ret;
   }
   return ret;
 }