Introduce the TYPEDEF element, and use it in order to catch passing closures to the DOM. I make the…

frog/leg/lib/js_helper.dart

Index: frog/leg/lib/js_helper.dart
===================================================================
--- frog/leg/lib/js_helper.dart	(revision 5070)
+++ frog/leg/lib/js_helper.dart	(working copy)
@@ -1305,6 +1305,27 @@
   return ex;
 }
 
+callClosure0(closure) => closure();
+callClosure1(closure, arg1) => closure(arg1);
+callClosure2(closure, arg1, arg2) => closure(arg1, arg2);
+
+convertDartClosureToJS(closure) {
+  return JS("var", @"""function() {
+    var dartClosure = $0;
+    switch (arguments.length) {
+      case 0: return $1(dartClosure);
+      case 1: return $2(dartClosure, arguments[0]);
+      case 2: return $3(dartClosure, arguments[0], arguments[1]);
+      default:
+        throw new Error('Unsupported number of arguments for wrapped closure');
+    }
+  }""",
+  closure,
+  callClosure0,
+  callClosure1,
+  callClosure2);
+}
+
 class StackTrace {
   var stack;
   StackTrace(this.stack);