A MessageObject is a purely internal object to hold information about

src/objects.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 36 matching lines @@
 //     - Smi          (immediate small integer)
 //     - HeapObject   (superclass for everything allocated in the heap)
 //       - JSObject
 //         - JSArray
 //         - JSRegExp
 //         - JSFunction
 //         - GlobalObject
 //           - JSGlobalObject
 //           - JSBuiltinsObject
 //         - JSGlobalProxy
-//        - JSValue
+//         - JSValue
+//         - JSMessageObject
 //       - ByteArray
 //       - PixelArray
 //       - ExternalArray
 //         - ExternalByteArray
 //         - ExternalUnsignedByteArray
 //         - ExternalShortArray
 //         - ExternalUnsignedShortArray
 //         - ExternalIntArray
 //         - ExternalUnsignedIntArray
 //         - ExternalFloatArray
@@ skipping 213 matching lines @@
   V(FUNCTION_TEMPLATE_INFO_TYPE)                                               \
   V(OBJECT_TEMPLATE_INFO_TYPE)                                                 \
   V(SIGNATURE_INFO_TYPE)                                                       \
   V(TYPE_SWITCH_INFO_TYPE)                                                     \
   V(SCRIPT_TYPE)                                                               \
   V(CODE_CACHE_TYPE)                                                           \
                                                                                \
   V(FIXED_ARRAY_TYPE)                                                          \
   V(SHARED_FUNCTION_INFO_TYPE)                                                 \
                                                                                \
+  V(JS_MESSAGE_OBJECT_TYPE)                                                    \
+                                                                               \
   V(JS_VALUE_TYPE)                                                             \
   V(JS_OBJECT_TYPE)                                                            \
   V(JS_CONTEXT_EXTENSION_OBJECT_TYPE)                                          \
   V(JS_GLOBAL_OBJECT_TYPE)                                                     \
   V(JS_BUILTINS_OBJECT_TYPE)                                                   \
   V(JS_GLOBAL_PROXY_TYPE)                                                      \
   V(JS_ARRAY_TYPE)                                                             \
   V(JS_REGEXP_TYPE)                                                            \
                                                                                \
   V(JS_FUNCTION_TYPE)                                                          \
@@ skipping 210 matching lines @@
   // The following two instance types are only used when ENABLE_DEBUGGER_SUPPORT
   // is defined. However as include/v8.h contain some of the instance type
   // constants always having them avoids them getting different numbers
   // depending on whether ENABLE_DEBUGGER_SUPPORT is defined or not.
   DEBUG_INFO_TYPE,
   BREAK_POINT_INFO_TYPE,
 
   FIXED_ARRAY_TYPE,
   SHARED_FUNCTION_INFO_TYPE,
 
+  JS_MESSAGE_OBJECT_TYPE,
+
   JS_VALUE_TYPE,  // FIRST_JS_OBJECT_TYPE
   JS_OBJECT_TYPE,
   JS_CONTEXT_EXTENSION_OBJECT_TYPE,
   JS_GLOBAL_OBJECT_TYPE,
   JS_BUILTINS_OBJECT_TYPE,
   JS_GLOBAL_PROXY_TYPE,
   JS_ARRAY_TYPE,
 
   JS_REGEXP_TYPE,  // LAST_JS_OBJECT_TYPE, FIRST_FUNCTION_CLASS_TYPE
 
@@ skipping 137 matching lines @@
   V(DeoptimizationOutputData)                  \
   V(FixedArray)                                \
   V(Context)                                   \
   V(CatchContext)                              \
   V(GlobalContext)                             \
   V(JSFunction)                                \
   V(Code)                                      \
   V(Oddball)                                   \
   V(SharedFunctionInfo)                        \
   V(JSValue)                                   \
+  V(JSMessageObject)                           \
   V(StringWrapper)                             \
   V(Proxy)                                     \
   V(Boolean)                                   \
   V(JSArray)                                   \
   V(JSRegExp)                                  \
   V(HashTable)                                 \
   V(Dictionary)                                \
   V(SymbolTable)                               \
   V(JSFunctionResultCache)                     \
   V(NormalizedMapCache)                        \
@@ skipping 4001 matching lines @@
 #endif
 
   // Layout description.
   static const int kValueOffset = JSObject::kHeaderSize;
   static const int kSize = kValueOffset + kPointerSize;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSValue);
 };
 
+
+// Representation of message objects used for error reporting through
+// the API. The messages are formatted in JavaScript so this object is
+// a real JavaScript object. The information used for formatting the
+// error messages are not directly accessible from JavaScript to
+// prevent leaking information to user code called during error
+// formatting.
+class JSMessageObject: public JSObject {
+ public:
+  // [type]: the type of error message.
+  DECL_ACCESSORS(type, String)
+
+  // [arguments]: the arguments for formatting the error message.
+  DECL_ACCESSORS(arguments, JSArray)
+
+  // [script]: the script from which the error message originated.
+  DECL_ACCESSORS(script, Object)
+
+  // [stack_trace]: the stack trace for this error message.
+  DECL_ACCESSORS(stack_trace, Object)
+
+  // [stack_frames]: an array of stack frames for this error object.
+  DECL_ACCESSORS(stack_frames, Object)
+
+  // [start_position]: the start position in the script for the error message.
+  inline int start_position();
+  inline void set_start_position(int value);
+
+  // [end_position]: the end position in the script for the error message.
+  inline int end_position();
+  inline void set_end_position(int value);
+
+  // Casting.
+  static inline JSMessageObject* cast(Object* obj);
+
+  // Dispatched behavior.
+#ifdef OBJECT_PRINT
+  inline void JSMessageObjectPrint() {
+    JSMessageObjectPrint(stdout);
+  }
+  void JSMessageObjectPrint(FILE* out);
+#endif
+#ifdef DEBUG
+  void JSMessageObjectVerify();
+#endif
+
+  // Layout description.
+  static const int kTypeOffset = JSObject::kHeaderSize;
+  static const int kArgumentsOffset = kTypeOffset + kPointerSize;
+  static const int kScriptOffset = kArgumentsOffset + kPointerSize;
+  static const int kStackTraceOffset = kScriptOffset + kPointerSize;
+  static const int kStackFramesOffset = kStackTraceOffset + kPointerSize;
+  static const int kStartPositionOffset = kStackFramesOffset + kPointerSize;
+  static const int kEndPositionOffset = kStartPositionOffset + kPointerSize;
+  static const int kSize = kEndPositionOffset + kPointerSize;
+
+  typedef FixedBodyDescriptor<HeapObject::kMapOffset,
+                              kStackFramesOffset + kPointerSize,
+                              kSize> BodyDescriptor;
+};
+
+
 // Regular expressions
 // The regular expression holds a single reference to a FixedArray in
 // the kDataOffset field.
 // The FixedArray contains the following data:
 // - tag : type of regexp implementation (not compiled yet, atom or irregexp)
 // - reference to the original source string
 // - reference to the original flag string
 // If it is an atom regexp
 // - a reference to a literal string to search for
 // If it is an irregexp regexp:
@@ skipping 1715 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_