Throw if setting length of a string in strict mode.

src/ic.cc

 // 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 1379 matching lines @@
                             StrictModeFlag strict_mode,
                             Handle<Object> object,
                             Handle<String> name,
                             Handle<Object> value) {
   // If the object is undefined or null it's illegal to try to set any
   // properties on it; throw a TypeError in that case.
   if (object->IsUndefined() || object->IsNull()) {
     return TypeError("non_object_property_store", object, name);
   }
 
-  // Ignore stores where the receiver is not a JSObject.
-  if (!object->IsJSObject()) return *value;
+  if (!object->IsJSObject()) {
+    // The length property of string values is read-only. Throw in strict mode.
+    if (strict_mode == kStrictMode && object->IsString() &&
+        name->Equals(Heap::length_symbol())) {
+      return TypeError("strict_read_only_property", object, name);
+    }
+    // Ignore stores where the receiver is not a JSObject.
+    return *value;
+  }
+
   Handle<JSObject> receiver = Handle<JSObject>::cast(object);
 
   // Check if the given name is an array index.
   uint32_t index;
   if (name->AsArrayIndex(&index)) {
     HandleScope scope;
     Handle<Object> result = SetElement(receiver, index, value, strict_mode);
     if (result.is_null()) return Failure::Exception();
     return *value;
   }
@@ skipping 912 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal