Properly handle primitive arguments in Object methods (#3342)

ES2015 allows primitive arguments for most of the Object built-ins.
This change implements handling for these arguments in affected methods.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

jerry-core/ecma/builtin-objects/ecma-builtin-object.c

@@ -40,23 +40,32 @@
 enum
 {
   ECMA_OBJECT_ROUTINE_START = ECMA_BUILTIN_ID__COUNT - 1,
-  ECMA_OBJECT_ROUTINE_DEFINE_PROPERTY,
+
-  ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_DESCRIPTOR,
-  ECMA_OBJECT_ROUTINE_DEFINE_PROPERTIES,
   ECMA_OBJECT_ROUTINE_CREATE,
-  ECMA_OBJECT_ROUTINE_SEAL,
+  ECMA_OBJECT_ROUTINE_IS,
-  ECMA_OBJECT_ROUTINE_FREEZE,
+  ECMA_OBJECT_ROUTINE_SET_PROTOTYPE_OF,
-  ECMA_OBJECT_ROUTINE_PREVENT_EXTENSIONS,
+
-  ECMA_OBJECT_ROUTINE_IS_SEALED,
+  /* These should be in this order. */
-  ECMA_OBJECT_ROUTINE_IS_FROZEN,
+  ECMA_OBJECT_ROUTINE_DEFINE_PROPERTY,
-  ECMA_OBJECT_ROUTINE_IS_EXTENSIBLE,
+  ECMA_OBJECT_ROUTINE_DEFINE_PROPERTIES,
+
+  /* These should be in this order. */
+  ECMA_OBJECT_ROUTINE_ASSIGN,
+  ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_DESCRIPTOR,
   ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_NAMES,
   ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_SYMBOLS,
-  ECMA_OBJECT_ROUTINE_KEYS,
   ECMA_OBJECT_ROUTINE_GET_PROTOTYPE_OF,
-  ECMA_OBJECT_ROUTINE_SET_PROTOTYPE_OF,
+  ECMA_OBJECT_ROUTINE_KEYS,
-  ECMA_OBJECT_ROUTINE_ASSIGN,
+
-  ECMA_OBJECT_ROUTINE_IS,
+  /* These should be in this order. */
+  ECMA_OBJECT_ROUTINE_FREEZE,
+  ECMA_OBJECT_ROUTINE_PREVENT_EXTENSIONS,
+  ECMA_OBJECT_ROUTINE_SEAL,
+
+  /* These should be in this order. */
+  ECMA_OBJECT_ROUTINE_IS_EXTENSIBLE,
+  ECMA_OBJECT_ROUTINE_IS_FROZEN,
+  ECMA_OBJECT_ROUTINE_IS_SEALED,
 };
 
 #define BUILTIN_INC_HEADER_NAME "ecma-builtin-object.inc.h"
@@ -125,47 +134,18 @@ ecma_builtin_object_dispatch_construct (const ecma_value_t *arguments_list_p, /*
  *         Returned value must be freed with ecma_free_value.
  */
 ecma_value_t
-ecma_builtin_object_object_get_prototype_of (ecma_value_t arg) /**< routine's argument */
+ecma_builtin_object_object_get_prototype_of (ecma_object_t *obj_p) /**< routine's argument */
 {
-  ecma_value_t ret_value = ECMA_VALUE_EMPTY;
-  bool was_object = ecma_is_value_object (arg);
-
-  /* 1. */
-  if (!was_object)
-  {
-#if ENABLED (JERRY_ES2015_BUILTIN)
-    arg = ecma_op_to_object (arg);
-    if (ECMA_IS_VALUE_ERROR (arg))
-    {
-      return arg;
-    }
-#else /* !ENABLED (JERRY_ES2015_BUILTIN) */
-    return ecma_raise_type_error (ECMA_ERR_MSG ("Argument is not an object."));
-#endif /* ENABLED (JERRY_ES2015_BUILTIN) */
-  }
-  /* 2. */
-  ecma_object_t *obj_p = ecma_get_object_from_value (arg);
   jmem_cpointer_t prototype_cp = obj_p->u2.prototype_cp;
 
   if (prototype_cp != JMEM_CP_NULL)
   {
     ecma_object_t *prototype_p = ECMA_GET_NON_NULL_POINTER (ecma_object_t, prototype_cp);
-    ret_value = ecma_make_object_value (prototype_p);
     ecma_ref_object (prototype_p);
-  }
+    return ecma_make_object_value (prototype_p);
-  else
-  {
-    ret_value = ECMA_VALUE_NULL;
   }
 
-#if ENABLED (JERRY_ES2015_BUILTIN)
+  return ECMA_VALUE_NULL;
-  if (!was_object)
-  {
-    ecma_deref_object (obj_p);
-  }
-#endif /* ENABLED (JERRY_ES2015_BUILTIN) */
-
-  return ret_value;
 } /* ecma_builtin_object_object_get_prototype_of */
 
 #if ENABLED (JERRY_ES2015_BUILTIN)
@@ -772,31 +752,14 @@ ecma_builtin_object_object_define_property (ecma_object_t *obj_p, /**< routine's
  *         Returned value must be freed with ecma_free_value.
  */
 static ecma_value_t
-ecma_builtin_object_object_assign (const ecma_value_t arguments_list_p[], /**< arguments list */
+ecma_builtin_object_object_assign (ecma_object_t *target_p, /**< target object */
+                                   const ecma_value_t arguments_list_p[], /**< arguments list */
                                    ecma_length_t arguments_list_len) /**< number of arguments */
 {
-  ecma_value_t target = arguments_list_len > 0 ? arguments_list_p[0] : ECMA_VALUE_UNDEFINED;
-
-  /* 1. */
-  ecma_value_t to_value = ecma_op_to_object (target);
-
-  if (ECMA_IS_VALUE_ERROR (to_value))
-  {
-    return to_value;
-  }
-
-  ecma_object_t *to_obj_p = ecma_get_object_from_value (to_value);
-
-  /* 2. */
-  if (arguments_list_len == 1)
-  {
-    return to_value;
-  }
-
   ecma_value_t ret_value = ECMA_VALUE_EMPTY;
 
   /* 4-5. */
-  for (uint32_t i = 1; i < arguments_list_len && ecma_is_value_empty (ret_value); i++)
+  for (uint32_t i = 0; i < arguments_list_len && ecma_is_value_empty (ret_value); i++)
   {
     ecma_value_t next_source = arguments_list_p[i];
 
@@ -848,7 +811,7 @@ ecma_builtin_object_object_assign (const ecma_value_t arguments_list_p[], /**< a
         else
         {
           /* 5.c.iii.3 */
-          ecma_value_t status = ecma_op_object_put (to_obj_p, property_name_p, prop_value, true);
+          ecma_value_t status = ecma_op_object_put (target_p, property_name_p, prop_value, true);
 
           /* 5.c.iii.4 */
           if (ECMA_IS_VALUE_ERROR (status))
@@ -869,10 +832,10 @@ ecma_builtin_object_object_assign (const ecma_value_t arguments_list_p[], /**< a
   /* 6. */
   if (ecma_is_value_empty (ret_value))
   {
-    return to_value;
+    ecma_ref_object (target_p);
+    return ecma_make_object_value (target_p);
   }
 
-  ecma_deref_object (to_obj_p);
   return ret_value;
 } /* ecma_builtin_object_object_assign */
 #endif /* ENABLED (JERRY_ES2015_BUILTIN) */
@@ -924,19 +887,11 @@ ecma_builtin_object_dispatch_routine (uint16_t builtin_routine_id, /**< built-in
     {
       return ecma_builtin_object_object_create (arg1, arg2);
     }
-    case ECMA_OBJECT_ROUTINE_GET_PROTOTYPE_OF:
-    {
-      return ecma_builtin_object_object_get_prototype_of (arg1);
-    }
 #if ENABLED (JERRY_ES2015_BUILTIN)
     case ECMA_OBJECT_ROUTINE_SET_PROTOTYPE_OF:
     {
       return ecma_builtin_object_object_set_prototype_of (arg1, arg2);
     }
-    case ECMA_OBJECT_ROUTINE_ASSIGN:
-    {
-      return ecma_builtin_object_object_assign (arguments_list_p, arguments_number);
-    }
     case ECMA_OBJECT_ROUTINE_IS:
     {
       return ecma_builtin_object_object_is (arg1, arg2);
@@ -948,83 +903,169 @@ ecma_builtin_object_dispatch_routine (uint16_t builtin_routine_id, /**< built-in
     }
   }
 
+  ecma_object_t *obj_p;
+#if !ENABLED (JERRY_ES2015)
   if (!ecma_is_value_object (arg1))
   {
     return ecma_raise_type_error (ECMA_ERR_MSG ("Argument is not an object."));
   }
+#endif /* !ENABLED (JERRY_ES2015) */
 
-  ecma_object_t *obj_p = ecma_get_object_from_value (arg1);
+  if (builtin_routine_id <= ECMA_OBJECT_ROUTINE_DEFINE_PROPERTIES)
-
-  if (builtin_routine_id <= ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_DESCRIPTOR)
   {
-    ecma_string_t *prop_name_p = ecma_op_to_prop_name (arg2);
+#if ENABLED (JERRY_ES2015)
-
+    if (!ecma_is_value_object (arg1))
-    if (prop_name_p == NULL)
     {
-      return ECMA_VALUE_ERROR;
+      return ecma_raise_type_error (ECMA_ERR_MSG ("Argument is not an object."));
     }
+#endif /* ENABLED (JERRY_ES2015) */
 
-    ecma_value_t ret_value;
+    obj_p = ecma_get_object_from_value (arg1);
 
     if (builtin_routine_id == ECMA_OBJECT_ROUTINE_DEFINE_PROPERTY)
     {
-      ret_value = ecma_builtin_object_object_define_property (obj_p, prop_name_p, arguments_list_p[2]);
+      ecma_string_t *prop_name_p = ecma_op_to_prop_name (arg2);
-    }
+
-    else
+      if (prop_name_p == NULL)
-    {
+      {
-      JERRY_ASSERT (builtin_routine_id == ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_DESCRIPTOR);
+        return ECMA_VALUE_ERROR;
-      ret_value = ecma_builtin_object_object_get_own_property_descriptor (obj_p, prop_name_p);
+      }
+
+      ecma_value_t result = ecma_builtin_object_object_define_property (obj_p, prop_name_p, arguments_list_p[2]);
+
+      ecma_deref_ecma_string (prop_name_p);
+      return result;
     }
 
-    ecma_deref_ecma_string (prop_name_p);
+    JERRY_ASSERT (builtin_routine_id == ECMA_OBJECT_ROUTINE_DEFINE_PROPERTIES);
-    return ret_value;
+    return ecma_builtin_object_object_define_properties (obj_p, arg2);
   }
-
+  else if (builtin_routine_id <= ECMA_OBJECT_ROUTINE_KEYS)
-  switch (builtin_routine_id)
   {
-    case ECMA_OBJECT_ROUTINE_SEAL:
-    {
-      return ecma_builtin_object_object_seal (obj_p);
-    }
-    case ECMA_OBJECT_ROUTINE_FREEZE:
-    {
-      return ecma_builtin_object_object_freeze (obj_p);
-    }
-    case ECMA_OBJECT_ROUTINE_PREVENT_EXTENSIONS:
-    {
-      return ecma_builtin_object_object_prevent_extensions (obj_p);
-    }
-    case ECMA_OBJECT_ROUTINE_IS_SEALED:
-    case ECMA_OBJECT_ROUTINE_IS_FROZEN:
-    {
-      return ecma_builtin_object_frozen_or_sealed_helper (obj_p,
-                                                          builtin_routine_id);
-    }
-    case ECMA_OBJECT_ROUTINE_IS_EXTENSIBLE:
-    {
-      return ecma_builtin_object_object_is_extensible (obj_p);
-    }
-    case ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_NAMES:
-    {
-      return ecma_builtin_object_object_get_own_property_names (obj_p);
-    }
 #if ENABLED (JERRY_ES2015)
-    case ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_SYMBOLS:
+    ecma_value_t object = ecma_op_to_object (arg1);
+    if (ECMA_IS_VALUE_ERROR (object))
     {
-      return ecma_builtin_object_object_get_own_property_symbols (obj_p);
+      return object;
+    }
+
+    obj_p = ecma_get_object_from_value (object);
+#else /* !ENABLED (JERRY_ES2015) */
+    obj_p = ecma_get_object_from_value (arg1);
+#endif /* ENABLED (JERRY_ES2015) */
+
+    ecma_value_t result;
+    switch (builtin_routine_id)
+    {
+      case ECMA_OBJECT_ROUTINE_GET_PROTOTYPE_OF:
+      {
+        result = ecma_builtin_object_object_get_prototype_of (obj_p);
+        break;
+      }
+      case ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_NAMES:
+      {
+        result = ecma_builtin_object_object_get_own_property_names (obj_p);
+        break;
+      }
+#if ENABLED (JERRY_ES2015)
+      case ECMA_OBJECT_ROUTINE_ASSIGN:
+      {
+        result = ecma_builtin_object_object_assign (obj_p, arguments_list_p + 1, arguments_number - 1);
+        break;
+      }
+      case ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_SYMBOLS:
+      {
+        result = ecma_builtin_object_object_get_own_property_symbols (obj_p);
+        break;
+      }
+#endif /* ENABLED (JERRY_ES2015) */
+      case ECMA_OBJECT_ROUTINE_KEYS:
+      {
+        result = ecma_builtin_object_object_keys (obj_p);
+        break;
+      }
+      case ECMA_OBJECT_ROUTINE_GET_OWN_PROPERTY_DESCRIPTOR:
+      {
+        ecma_string_t *prop_name_p = ecma_op_to_prop_name (arg2);
+
+        if (prop_name_p == NULL)
+        {
+          result = ECMA_VALUE_ERROR;
+          break;
+        }
+
+        result = ecma_builtin_object_object_get_own_property_descriptor (obj_p, prop_name_p);
+        ecma_deref_ecma_string (prop_name_p);
+        break;
+      }
+      default:
+      {
+        JERRY_UNREACHABLE ();
+      }
+    }
+
+#if ENABLED (JERRY_ES2015)
+    ecma_deref_object (obj_p);
+#endif /* ENABLED (JERRY_ES2015) */
+    return result;
+  }
+  else if (builtin_routine_id <= ECMA_OBJECT_ROUTINE_SEAL)
+  {
+#if ENABLED (JERRY_ES2015)
+    if (!ecma_is_value_object (arg1))
+    {
+      return arg1;
     }
 #endif /* ENABLED (JERRY_ES2015) */
-    case ECMA_OBJECT_ROUTINE_KEYS:
+
+    obj_p = ecma_get_object_from_value (arg1);
+    switch (builtin_routine_id)
     {
-      return ecma_builtin_object_object_keys (obj_p);
+      case ECMA_OBJECT_ROUTINE_SEAL:
+      {
+        return ecma_builtin_object_object_seal (obj_p);
+      }
+      case ECMA_OBJECT_ROUTINE_FREEZE:
+      {
+        return ecma_builtin_object_object_freeze (obj_p);
+      }
+      case ECMA_OBJECT_ROUTINE_PREVENT_EXTENSIONS:
+      {
+        return ecma_builtin_object_object_prevent_extensions (obj_p);
+      }
+      default:
+      {
+        JERRY_UNREACHABLE ();
+      }
     }
-    case ECMA_OBJECT_ROUTINE_DEFINE_PROPERTIES:
+  }
+  else
+  {
+    JERRY_ASSERT (builtin_routine_id <= ECMA_OBJECT_ROUTINE_IS_SEALED);
+#if ENABLED (JERRY_ES2015)
+    if (!ecma_is_value_object (arg1))
     {
-      return ecma_builtin_object_object_define_properties (obj_p, arg2);
+      return ecma_make_boolean_value (builtin_routine_id != ECMA_OBJECT_ROUTINE_IS_EXTENSIBLE);
     }
-    default:
+#endif /* ENABLED (JERRY_ES2015) */
+
+    obj_p = ecma_get_object_from_value (arg1);
+    switch (builtin_routine_id)
     {
-      JERRY_UNREACHABLE ();
+      case ECMA_OBJECT_ROUTINE_IS_SEALED:
+      case ECMA_OBJECT_ROUTINE_IS_FROZEN:
+      {
+        return ecma_builtin_object_frozen_or_sealed_helper (obj_p,
+                                                            builtin_routine_id);
+      }
+      case ECMA_OBJECT_ROUTINE_IS_EXTENSIBLE:
+      {
+        return ecma_builtin_object_object_is_extensible (obj_p);
+      }
+      default:
+      {
+        JERRY_UNREACHABLE ();
+      }
     }
   }
 } /* ecma_builtin_object_dispatch_routine */

jerry-core/ecma/builtin-objects/ecma-builtin-object.h

@@ -15,7 +15,7 @@
 #ifndef ECMA_BUILTIN_OBJECT_H
 #define ECMA_BUILTIN_OBJECT_H
 
-ecma_value_t ecma_builtin_object_object_get_prototype_of (ecma_value_t arg);
+ecma_value_t ecma_builtin_object_object_get_prototype_of (ecma_object_t *obj_p);
 
 ecma_value_t ecma_builtin_object_object_set_prototype_of (ecma_value_t arg1,
                                                           ecma_value_t arg2);

jerry-core/ecma/builtin-objects/ecma-builtin-reflect.c

@@ -87,7 +87,7 @@ ecma_builtin_reflect_dispatch_routine (uint16_t builtin_routine_id, /**< built-i
   {
     case ECMA_REFLECT_OBJECT_GET_PROTOTYPE_OF_UL:
     {
-      return ecma_builtin_object_object_get_prototype_of (arguments_list[0]);
+      return ecma_builtin_object_object_get_prototype_of (ecma_get_object_from_value (arguments_list[0]));
     }
     case ECMA_REFLECT_OBJECT_SET_PROTOTYPE_OF_UL:
     {

tests/jerry/es2015/object-get-own-property-symbols.js

@@ -109,11 +109,3 @@ assert (props.indexOf(foo2) !== -1);
 assert (props.length === 2);
 assert (Object.getOwnPropertyDescriptor (object, foo).enumerable === true);
 assert (Object.getOwnPropertyDescriptor (object, foo2).enumerable === false);
-
-// Test non-object argument
-try {
-  Object.getOwnPropertySymbols ('hello');
-  assert (false);
-} catch (e) {
-  assert (e instanceof TypeError);
-}

tests/jerry/es2015/object-methods.js

@@ -0,0 +1,48 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+assert (JSON.stringify (Object.getOwnPropertyNames("hello")) === '["0","1","2","3","4","length"]');
+
+var n = Object.assign(42, {a: "str"});
+assert (n instanceof Number);
+assert (n.valueOf() === 42);
+assert (n.a === "str");
+
+assert (JSON.stringify (Object.getOwnPropertySymbols("hello")) === '[]');
+
+assert (JSON.stringify (Object.keys("str")) === '["0","1","2"]');
+
+var d = Object.getOwnPropertyDescriptor("hello", '1');
+assert (d.value === "e");
+assert (d.writable === false);
+assert (d.enumerable === true);
+assert (d.configurable === false);
+
+assert (Object.seal(42) === 42);
+assert (Object.seal(undefined) === undefined);
+
+assert (Object.isSealed(42) === true);
+assert (Object.isSealed(undefined) === true);
+
+assert (Object.freeze(42) === 42);
+assert (Object.freeze(undefined) === undefined);
+
+assert (Object.isFrozen(42) === true);
+assert (Object.isFrozen(undefined) === true);
+
+assert (Object.preventExtensions(42) === 42);
+assert (Object.preventExtensions(undefined) === undefined);
+
+assert (Object.isExtensible(42) === false);
+assert (Object.isExtensible(undefined) === false);

tests/jerry/es5.1/object-methods.js

@@ -0,0 +1,89 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+try {
+  Object.getOwnPropertyNames("hello");
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.preventExtensions(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.isExtensible(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.seal(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.isSealed(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.freeze(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try
+{
+  Object.isFrozen(42);
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try {
+  Object.keys("hello");
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try {
+  Object.getOwnPropertyNames("hello");
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}
+
+try {
+  Object.getOwnPropertyDescriptor("hello", '1');
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}

tests/jerry/object-defineproperty.js

@@ -68,3 +68,12 @@ try {
 } catch (err) {
   assert (err === 234);
 }
+
+try {
+  Object.defineProperty(42, "prop", {
+      set: undefined
+  });
+  assert (false);
+} catch (e) {
+  assert (e instanceof TypeError);
+}

tests/jerry/object-get-own-property-names.js

@@ -62,11 +62,3 @@ assert (props.indexOf("prop") !== -1);
 assert (props.indexOf("method") !== -1);
 
 assert (props.length === 2);
-
-// Test non-object argument
-try {
-  Object.getOwnPropertyNames("hello");
-  assert (false);
-} catch (e) {
-  assert (e instanceof TypeError);
-}

tests/jerry/object-is-extensible.js

@@ -20,23 +20,6 @@ assert (Object.isExtensible(empty) === true);
 Object.preventExtensions(empty);
 assert(Object.isExtensible(empty) === false);
 
-// Call on undefined should throw TypeError.
-try
-{
-    Object.isExtensible(undefined);
-    assert (false);
-} catch (e) {
-    assert (e instanceof TypeError);
-}
-
-try
-{
-    Object.preventExtensions(undefined);
-    assert (false);
-} catch (e) {
-    assert (e instanceof TypeError);
-}
-
 // Sealed objects are by definition non-extensible.
 var sealed = Object.seal({});
 assert (Object.isExtensible(sealed) === false);

tests/jerry/object-keys.js

@@ -61,14 +61,6 @@ assert (props.indexOf("prop") !== -1);
 assert (props.indexOf("method") !== -1);
 assert (props.length === 2);
 
-// Test non-object argument
-try {
-  Object.keys("hello");
-  assert (false);
-} catch (e) {
-  assert (e instanceof TypeError);
-}
-
 var o = {};
 
 Object.defineProperty(o, 'a', {