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

 // Copyright (c) 2012, 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.
 
 #library('js_helper');
 
 #import('coreimpl.dart');
 
 #source('date_helper.dart');
 #source('regexp_helper.dart');
@@ skipping 1287 matching lines @@
     }
   } else if (JS('bool', @'$0 instanceof RangeError', ex)) {
     var message = JS('String', @'$0.message', ex);
     if (message.contains('call stack')) {
       return new StackOverflowException();
     }
   }
   return ex;
 }
 
-class StackTrace {
-  var stack;
-  StackTrace(this.stack);
-  String toString() => stack != null ? stack : '';
-}
-
 /**
  * Called by generated code to fetch the stack trace from an
  * exception.
  */
 StackTrace getTraceFromException(exception) {
   return new StackTrace(JS("var", @"$0.stack", exception));
 }
 
 /**
  * Called by generated code to build a map literal. [keyValuePairs] is
  * a list of key, value, key, value, ..., etc.
  */
 makeLiteralMap(List keyValuePairs) {
   Iterator iterator = keyValuePairs.iterator();
   Map result = new LinkedHashMap();
   while (iterator.hasNext()) {
     String key = iterator.next();
     var value = iterator.next();
     result[key] = value;
   }
   return result;
 }
+
+/**
+ * Called by generated code to convert a Dart closure to a JS
+ * closure when the Dart closure is passed to the DOM.
+ */
+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);
+}
+
+/**
+ * Helper methods when converting a Dart closure to a JS closure.
+ */
+callClosure0(closure) => closure();
+callClosure1(closure, arg1) => closure(arg1);
+callClosure2(closure, arg1, arg2) => closure(arg1, arg2);
+
+class StackTrace {
+  var stack;
+  StackTrace(this.stack);
+  String toString() => stack != null ? stack : '';
+}