diff -r 6e8e00258234 -r cb0cfba1b863 src/main/java/org/apidesign/java4browser/ByteCodeToJavaScript.java
--- a/src/main/java/org/apidesign/java4browser/ByteCodeToJavaScript.java	Thu Sep 20 10:26:59 2012 +0200
+++ b/src/main/java/org/apidesign/java4browser/ByteCodeToJavaScript.java	Thu Sep 20 10:39:54 2012 +0200
@@ -82,6 +82,7 @@
                 out.append("\n  this." + v.getName() + " = 0;");
             }
         }
+        out.append("\n  this.$instOf_").append(className).append(" = true;");
         out.append("\n}");
         ClassName sc = jc.getSuperClass();
         if (sc != null) {
@@ -446,6 +447,14 @@
                     i += 2;
                     break;
                 }
+                case bc_instanceof: {
+                    int indx = readIntArg(byteCodes, i);
+                    CPClassInfo ci = jc.getConstantPool().getClass(indx);
+                    out.append("stack.push(stack.pop().$instOf_")
+                       .append(ci.getClassName().getExternalName().replace('.', '_'))
+                       .append(" ? 1 : 0);");
+                    i += 2;
+                }
                     
             }
             out.append(" /*");