Array length reduction should throw in strict mode if it can't delete an element.

src/accessors.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/accessors.h"
 
 #include "src/api.h"
 #include "src/contexts.h"
 #include "src/deoptimizer.h"
 #include "src/execution.h"
@@ skipping 186 matching lines @@
 
   uint32_t length = 0;
   if (!JSArray::AnythingToArrayLength(isolate, length_obj, &length)) {
     isolate->OptionalRescheduleException(false);
     return;
   }
 
   if (JSArray::ObservableSetLength(array, length).is_null()) {
     isolate->OptionalRescheduleException(false);
   }
+
+  if (info.ShouldThrowOnError()) {
+    uint32_t actual_new_len = 0;
+    CHECK(array->length()->ToArrayLength(&actual_new_len));
+    // Throw TypeError if there were non-deletable elements.
+    if (actual_new_len != length) {
+      Factory* factory = isolate->factory();
+      isolate->Throw(*factory->NewTypeError(
+          MessageTemplate::kStrictDeleteProperty,
+          factory->NewNumberFromUint(actual_new_len - 1), array));
+      isolate->OptionalRescheduleException(false);
+    }
+  }
 }
 
 
 Handle<AccessorInfo> Accessors::ArrayLengthInfo(
       Isolate* isolate, PropertyAttributes attributes) {
   return MakeAccessor(isolate,
                       isolate->factory()->length_string(),
                       &ArrayLengthGetter,
                       &ArrayLengthSetter,
                       attributes);
@@ skipping 1180 matching lines @@
     isolate->ScheduleThrow(*exception);
     return;
   }
   info.GetReturnValue().Set(v8::Utils::ToLocal(Handle<Object>(value, isolate)));
 }
 
 
 static void ModuleSetExport(v8::Local<v8::Name> property,
                             v8::Local<v8::Value> value,
                             const v8::PropertyCallbackInfo<void>& info) {
+  if (!info.ShouldThrowOnError()) return;
   Handle<Name> name = v8::Utils::OpenHandle(*property);
   Isolate* isolate = name->GetIsolate();
   Handle<Object> exception =
       isolate->factory()->NewTypeError(MessageTemplate::kNotDefined, name);
   isolate->ScheduleThrow(*exception);
 }
 
 
 Handle<AccessorInfo> Accessors::MakeModuleExport(
     Handle<String> name,
     int index,
     PropertyAttributes attributes) {
   Isolate* isolate = name->GetIsolate();
   Handle<AccessorInfo> info = MakeAccessor(isolate, name, &ModuleGetExport,
                                            &ModuleSetExport, attributes);
   info->set_data(Smi::FromInt(index));
   return info;
 }
 
 
 }  // namespace internal
 }  // namespace v8