diff -r 24096bd2b38a -r b8e33a00bfab rt/emul/mini/src/main/java/org/apidesign/bck2brwsr/emul/lang/System.java
--- a/rt/emul/mini/src/main/java/org/apidesign/bck2brwsr/emul/lang/System.java	Sun Mar 10 21:28:50 2013 +0100
+++ b/rt/emul/mini/src/main/java/org/apidesign/bck2brwsr/emul/lang/System.java	Thu Jan 09 08:21:26 2014 +0100
@@ -19,6 +19,7 @@
 
 import java.lang.reflect.Method;
 import org.apidesign.bck2brwsr.core.JavaScriptBody;
+import org.apidesign.bck2brwsr.core.JavaScriptOnly;
 
 /**
  *
@@ -71,4 +72,27 @@
     }
     @JavaScriptBody(args = { "obj" }, body="return vm.java_lang_Object(false).hashCode__I.call(obj);")
     public static native int identityHashCode(Object obj);
+    
+    @JavaScriptOnly(name = "toJS", value = "function(v) {\n" + 
+        "  if (v === null) return null;\n" +
+        "  if (Object.prototype.toString.call(v) === '[object Array]') {\n" +
+        "    return vm.org_apidesign_bck2brwsr_emul_lang_System(false).convArray__Ljava_lang_Object_2Ljava_lang_Object_2(v);\n" +
+        "  }\n" +
+        "  return v.valueOf();\n" +
+        "}\n"
+    )
+    public static native int toJS();
+    
+    private static Object convArray(Object o) {
+        if (o instanceof Object[]) {
+            Object[] arr = (Object[]) o;
+            final int l = arr.length;
+            Object[] ret = new Object[l];
+            for (int i = 0; i < l; i++) {
+                ret[i] = convArray(arr[i]);
+            }
+            return ret;
+        }
+        return o;
+    }
 }