Use the typedef arity to know how to invoke a closure given by the dom.

dart/lib/compiler/implementation/lib/js_helper.dart

Index: dart/lib/compiler/implementation/lib/js_helper.dart
===================================================================
--- dart/lib/compiler/implementation/lib/js_helper.dart	(revision 8049)
+++ dart/lib/compiler/implementation/lib/js_helper.dart	(working copy)
@@ -850,17 +850,18 @@
  * Called by generated code to convert a Dart closure to a JS
  * closure when the Dart closure is passed to the DOM.
  */
-convertDartClosureToJS(closure) {
+convertDartClosureToJS(closure, int numberOfArguments) {

[kasperl, 2012/05/29 12:16:24]

numberOfArguments -> arity?

[ngeoffray, 2012/05/29 12:31:01]

Done.

   if (closure === null) return null;
   var function = JS('var', @'#.$identity', closure);
   if (JS('bool', @'!!#', function)) return function;
 
   function = JS("var", @"""function() {
-    return #(#, #, arguments.length, arguments[0], arguments[1]);
+    return #(#, #, #, arguments[0], arguments[1]);
   }""",
   DART_CLOSURE_TO_JS(invokeClosure),
   closure,
-  JS_CURRENT_ISOLATE());
+  JS_CURRENT_ISOLATE(),
+  numberOfArguments);
 
   JS('void', @'#.$identity = #', closure, function);
   return function;