@@ -17,18 +17,26 @@ using v8::Local;
 using v8::Object;
 using v8::Value;
 
+static void ThrowEventError(v8::Isolate* isolate, const std::string& message) {
+  isolate->ThrowException(v8::Exception::TypeError(
+      v8::String::NewFromUtf8(isolate, message.c_str()).ToLocalChecked()));
+}
+
 std::unique_ptr<protocol::DOMStorage::StorageId> createStorageIdFromObject(
     Local<Context> context, Local<Object> storage_id_obj) {
   protocol::String security_origin;
+  Isolate* isolate = Isolate::GetCurrent();
   if (!ObjectGetProtocolString(context, storage_id_obj, "securityOrigin")
            .To(&security_origin)) {
+    ThrowEventError(isolate, "Missing securityOrigin in storageId");
     return {};
   }
   bool is_local_storage =
       ObjectGetBool(context, storage_id_obj, "isLocalStorage").FromMaybe(false);
   protocol::String storageKey;
   if (!ObjectGetProtocolString(context, storage_id_obj, "storageKey")
            .To(&storageKey)) {
+    ThrowEventError(isolate, "Missing storageKey in storageId");
     return {};
   }
 
@@ -135,8 +143,10 @@ protocol::DispatchResponse DOMStorageAgent::clear(
 
 void DOMStorageAgent::domStorageItemAdded(Local<Context> context,
                                           Local<Object> params) {
+  Isolate* isolate = env_->isolate();
   Local<Object> storage_id_obj;
   if (!ObjectGetObject(context, params, "storageId").ToLocal(&storage_id_obj)) {
+    ThrowEventError(isolate, "Missing storageId in event");
     return;
   }
 
@@ -148,19 +158,23 @@ void DOMStorageAgent::domStorageItemAdded(Local<Context> context,
 
   protocol::String key;
   if (!ObjectGetProtocolString(context, params, "key").To(&key)) {
+    ThrowEventError(isolate, "Missing key in event");
     return;
   }
   protocol::String new_value;
   if (!ObjectGetProtocolString(context, params, "newValue").To(&new_value)) {
+    ThrowEventError(isolate, "Missing newValue in event");
     return;
   }
   frontend_->domStorageItemAdded(std::move(storage_id), key, new_value);
 }
 
 void DOMStorageAgent::domStorageItemRemoved(Local<Context> context,
                                             Local<Object> params) {
+  Isolate* isolate = env_->isolate();
   Local<Object> storage_id_obj;
   if (!ObjectGetObject(context, params, "storageId").ToLocal(&storage_id_obj)) {
+    ThrowEventError(isolate, "Missing storageId in event");
     return;
   }
   std::unique_ptr<protocol::DOMStorage::StorageId> storage_id =
@@ -172,15 +186,18 @@ void DOMStorageAgent::domStorageItemRemoved(Local<Context> context,
 
   protocol::String key;
   if (!ObjectGetProtocolString(context, params, "key").To(&key)) {
+    ThrowEventError(isolate, "Missing key in event");
     return;
   }
   frontend_->domStorageItemRemoved(std::move(storage_id), key);
 }
 
 void DOMStorageAgent::domStorageItemUpdated(Local<Context> context,
                                             Local<Object> params) {
+  Isolate* isolate = env_->isolate();
   Local<Object> storage_id_obj;
   if (!ObjectGetObject(context, params, "storageId").ToLocal(&storage_id_obj)) {
+    ThrowEventError(isolate, "Missing storageId in event");
     return;
   }
 
@@ -193,14 +210,17 @@ void DOMStorageAgent::domStorageItemUpdated(Local<Context> context,
 
   protocol::String key;
   if (!ObjectGetProtocolString(context, params, "key").To(&key)) {
+    ThrowEventError(isolate, "Missing key in event");
     return;
   }
   protocol::String old_value;
   if (!ObjectGetProtocolString(context, params, "oldValue").To(&old_value)) {
+    ThrowEventError(isolate, "Missing oldValue in event");
     return;
   }
   protocol::String new_value;
   if (!ObjectGetProtocolString(context, params, "newValue").To(&new_value)) {
+    ThrowEventError(isolate, "Missing newValue in event");
     return;
   }
   frontend_->domStorageItemUpdated(
@@ -209,8 +229,10 @@ void DOMStorageAgent::domStorageItemUpdated(Local<Context> context,
 
 void DOMStorageAgent::domStorageItemsCleared(Local<Context> context,
                                              Local<Object> params) {
+  Isolate* isolate = env_->isolate();
   Local<Object> storage_id_obj;
   if (!ObjectGetObject(context, params, "storageId").ToLocal(&storage_id_obj)) {
+    ThrowEventError(isolate, "Missing storageId in event");
     return;
   }
   std::unique_ptr<protocol::DOMStorage::StorageId> storage_id =
@@ -228,27 +250,32 @@ void DOMStorageAgent::registerStorage(Local<Context> context,
   HandleScope handle_scope(isolate);
   bool is_local_storage;
   if (!ObjectGetBool(context, params, "isLocalStorage").To(&is_local_storage)) {
+    ThrowEventError(isolate, "Missing isLocalStorage in event");
     return;
   }
   Local<Object> storage_map_obj;
   if (!ObjectGetObject(context, params, "storageMap")
            .ToLocal(&storage_map_obj)) {
+    ThrowEventError(isolate, "Missing storageMap in event");
     return;
   }
   StorageMap& storage_map =
       is_local_storage ? local_storage_map_ : session_storage_map_;
   Local<Array> property_names;
   if (!storage_map_obj->GetOwnPropertyNames(context).ToLocal(&property_names)) {
+    ThrowEventError(isolate, "Failed to get property names from storageMap");
     return;
   }
   uint32_t length = property_names->Length();
   for (uint32_t i = 0; i < length; ++i) {
     Local<Value> key_value;
     if (!property_names->Get(context, i).ToLocal(&key_value)) {
+      ThrowEventError(isolate, "Failed to get key from storageMap");
       return;
     }
     Local<Value> value_value;
     if (!storage_map_obj->Get(context, key_value).ToLocal(&value_value)) {
+      ThrowEventError(isolate, "Failed to get value from storageMap");
       return;
     }
     node::TwoByteValue key_utf16(isolate, key_value);