Generator objects have [[Class]] === "Generator"

src/macros.py

 # Copyright 2006-2009 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 99 matching lines @@
 macro IS_DATE(arg)              = (%_ClassOf(arg) === 'Date');
 macro IS_NUMBER_WRAPPER(arg)    = (%_ClassOf(arg) === 'Number');
 macro IS_STRING_WRAPPER(arg)    = (%_ClassOf(arg) === 'String');
 macro IS_SYMBOL_WRAPPER(arg)    = (%_ClassOf(arg) === 'Symbol');
 macro IS_BOOLEAN_WRAPPER(arg)   = (%_ClassOf(arg) === 'Boolean');
 macro IS_ERROR(arg)             = (%_ClassOf(arg) === 'Error');
 macro IS_SCRIPT(arg)            = (%_ClassOf(arg) === 'Script');
 macro IS_ARGUMENTS(arg)         = (%_ClassOf(arg) === 'Arguments');
 macro IS_GLOBAL(arg)            = (%_ClassOf(arg) === 'global');
 macro IS_ARRAYBUFFER(arg)       = (%_ClassOf(arg) === '__ArrayBuffer');
+macro IS_GENERATOR(arg)         = (%_ClassOf(arg) === 'Generator');
 macro IS_UNDETECTABLE(arg)      = (%_IsUndetectableObject(arg));
 macro FLOOR(arg)                = $floor(arg);
 
 # Macro for ECMAScript 5 queries of the type:
 # "Type(O) is object."
 # This is the same as being either a function or an object in V8 terminology
 # (including proxies).
 # In addition, an undetectable object is also included by this.
 macro IS_SPEC_OBJECT(arg)   = (%_IsSpecObject(arg));
 
@@ skipping 106 matching lines @@
 const TYPE_EXTENSION = 1;
 const TYPE_NORMAL = 2;
 
 # Matches Script::CompilationType from objects.h
 const COMPILATION_TYPE_HOST = 0;
 const COMPILATION_TYPE_EVAL = 1;
 const COMPILATION_TYPE_JSON = 2;
 
 # Matches Messages::kNoLineNumberInfo from v8.h
 const kNoLineNumberInfo = 0;