diff --git a/cpp/platform_support/dom_connector.hpp b/cpp/platform_support/dom_connector.hpp
index 3daf3b6..6268f35 100644
--- a/cpp/platform_support/dom_connector.hpp
+++ b/cpp/platform_support/dom_connector.hpp
@@ -11,6 +11,7 @@
 #include <memory>
 
 struct JsStub;
+struct JsFuncStub;
 class JsObjectTempRef;
 using JsObjectRef = std::shared_ptr<JsObjectTempRef>;
 
@@ -18,19 +19,21 @@ extern "C" {
 /**
  * @brief Increments the refcount of an opaque JavaScript object ID.
  */
-extern void _js_ref(unsigned int obj);
+extern void _js_ref(unsigned int obj_id);
 
 /**
  * @brief Decrements the refcount of an opaque JavaScript object ID.
  * 
  * When the refcount reaches zero the object ID must not be used anymore.
  */
-extern void _js_unref(unsigned int obj);
+extern void _js_unref(unsigned int obj_id);
 
-extern void _js_call_sync(unsigned int obj, const char* func, JsStub* args, size_t n_args);
-extern void _js_call_async(unsigned int obj, const char* func, JsStub* args, size_t n_args, void(*callback)(void*, const JsStub&), void* ctx, unsigned int dict_depth);
-extern void _js_get_property(unsigned int obj, const char* property, void(*callback)(void*, const JsStub&), void* ctx, unsigned int dict_depth);
-extern void _js_set_property(unsigned int obj, const char* property, JsStub* arg);
+extern void* _js_get_property(unsigned int obj_id, const char* property, unsigned int dict_depth, JsStub* p_out);
+extern void _js_set_property(unsigned int obj_id, const char* property, JsStub* arg);
+extern void* _js_call_sync(unsigned int obj_id, const char* func, JsStub* args, size_t n_args, unsigned int dict_depth, JsStub* p_out);
+extern void _js_call_async(unsigned int obj_id, const char* func, JsStub* args, size_t n_args, void(*callback)(void*, const JsStub&, const JsStub&), void* ctx, unsigned int dict_depth);
+
+extern void _js_release(void*);
 }
 
 
@@ -53,10 +56,11 @@ struct JsStub {
 struct JsFuncStub {
     uintptr_t callback;
     uintptr_t ctx;
+    unsigned int dict_depth;
 };
 
 struct JsArrayStub {
-    uintptr_t start;
+    uintptr_t begin;
     uintptr_t end;
 };
 
@@ -75,7 +79,10 @@ class JsTransferStorage {
             delete [] ptr;
         }
         for (auto ptr: funcs) {
-            delete [] ptr;
+            delete ptr;
+        }
+        for (auto ptr: arrays) {
+            delete ptr;
         }
     }
 
@@ -115,7 +122,7 @@ class JsTransferStorage {
     }
 
     JsStub to_js(fibre::Callback<void, const JsStub*, size_t> val) {
-        JsFuncStub* func = new JsFuncStub{(uintptr_t)val.get_ptr(), (uintptr_t)val.get_ctx()};
+        JsFuncStub* func = new JsFuncStub{(uintptr_t)val.get_ptr(), (uintptr_t)val.get_ctx(), 0};
         funcs.push_back(func);
         return {JsType::kFunc, (uintptr_t)func};
     }
@@ -146,14 +153,10 @@ class JsObjectTempRef {
     }
 
     template<typename TVal> fibre::RichStatus get_property(std::string property, TVal* result, unsigned int dict_depth = 0) {
-        fibre::RichStatus status;
-        fibre::Callback<void, const JsStub&> callback{
-            [&](const JsStub& stub) {
-                status = from_js(stub, result);
-            }
-        };
-        _js_get_property(id_, property.data(), callback.get_ptr(),
-                         callback.get_ctx(), dict_depth);
+        JsStub out;
+        void* storage = _js_get_property(id_, property.data(), dict_depth, &out);
+        fibre::RichStatus status = from_js(out, result);
+        _js_release(storage);
         return status;
     }
 
@@ -172,7 +175,7 @@ class JsObjectTempRef {
 
     template<typename... TArgs>
     void call_async(std::string func,
-                    fibre::Callback<void, const JsStub&> callback,
+                    fibre::Callback<void, const JsStub&, const JsStub&> callback,
                     unsigned int dict_depth,
                     TArgs... args) {
         JsTransferStorage storage;
@@ -266,7 +269,7 @@ static inline fibre::RichStatus from_js(const JsStub& stub, fibre::cbufptr_t* ou
     // time allocated buffer. Maybe we can optimize this?
     F_RET_IF(stub.type != JsType::kArray, "expected array type but got " << (int)stub.type);
     JsArrayStub* array_stub = (JsArrayStub*)stub.val;
-    *output = {(const unsigned char*)array_stub->start, (const unsigned char*)array_stub->end};
+    *output = {(const unsigned char*)array_stub->begin, (const unsigned char*)array_stub->end};
     return fibre::RichStatus::success();
 }
 
diff --git a/cpp/platform_support/dom_connector.js b/cpp/platform_support/dom_connector.js
index fc538a2..387a688 100644
--- a/cpp/platform_support/dom_connector.js
+++ b/cpp/platform_support/dom_connector.js
@@ -170,7 +170,7 @@ mergeInto(LibraryManager.library, {
       const cb = Module.asm.__indirect_function_table.get(callback);
       const storage = makeStorage();
       try {
-        const ptr = Module._malloc(8 + args.length);
+        const ptr = Module._malloc(8 * args.length);
         try {
           for (let i = 0; i < args.length; ++i) {
             toWasm(storage, args[i], ptr + 8 * i);
@@ -215,19 +215,22 @@ mergeInto(LibraryManager.library, {
 
     __js_ref = _js_ref;
     __js_unref = _js_unref;
-    __js_call_async = _js_call_async;
     __js_get_property = _js_get_property;
     __js_set_property = _js_set_property;
+    __js_call_async = _js_call_async;
+    __js_release = _js_release;
   },
 
   _js_ref: function() {},
   _js_ref__deps: ['$method_support'],
   _js_unref: function() {},
   _js_unref__deps: ['$method_support'],
-  _js_call_async: function() {},
-  _js_call_async__deps: ['$method_support'],
   _js_get_property: function() {},
   _js_get_property__deps: ['$method_support'],
   _js_set_property: function() {},
   _js_set_property__deps: ['$method_support'],
+  _js_call_async: function() {},
+  _js_call_async__deps: ['$method_support'],
+  _js_release: function() {},
+  _js_release__deps: ['$method_support'],
 });
diff --git a/cpp/platform_support/webusb_backend.cpp b/cpp/platform_support/webusb_backend.cpp
index 964d3c8..60ef9ca 100644
--- a/cpp/platform_support/webusb_backend.cpp
+++ b/cpp/platform_support/webusb_backend.cpp
@@ -30,7 +30,7 @@ class WebUsb final : public UsbHostController {
                      on_lost_device_t on_lost) final;
     RichStatus stop() final;
 
-    void on_get_devices_finished(const JsStub& stub);
+    void on_get_devices_finished(const JsStub& result_stub, const JsStub& error_stub);
     void on_connect(const JsStub* args, size_t n_args);
     void on_disconnect(const JsStub* args, size_t n_args);
 
@@ -51,10 +51,10 @@ struct WebUsbDevice final : UsbDevice {
     RichStatus bulk_in_transfer(uint8_t ep_num, bufptr_t buffer, Callback<void, RichStatus, unsigned char*> callback) final;
     RichStatus bulk_out_transfer(uint8_t ep_num, cbufptr_t buffer, Callback<void, RichStatus, const unsigned char*> callback) final;
 
-    void on_open_finished(const JsStub& stub);
-    void on_claim_interface_finished(const JsStub& stub);
-    void on_bulk_in_transfer_finished(const JsStub& stub);
-    void on_bulk_out_transfer_finished(const JsStub& stub);
+    void on_open_finished(const JsStub& result_stub, const JsStub& error_stub);
+    void on_claim_interface_finished(const JsStub& result_stub, const JsStub& error_stub);
+    void on_bulk_in_transfer_finished(const JsStub& result_stub, const JsStub& error_stub);
+    void on_bulk_out_transfer_finished(const JsStub& result_stub, const JsStub& error_stub);
 
     WebUsb* webusb_;
     JsObjectRef ref_;
@@ -101,11 +101,11 @@ RichStatus WebUsb::stop() {
     return RichStatus::success();
 }
 
-void WebUsb::on_get_devices_finished(const JsStub& stub) {
+void WebUsb::on_get_devices_finished(const JsStub& result_stub, const JsStub& error_stub) {
     F_LOG_D(logger_, "got devices");
 
     std::vector<JsObjectRef> devices;
-    if (F_LOG_IF_ERR(logger_, from_js(stub, &devices), "in device list")) {
+    if (F_LOG_IF_ERR(logger_, from_js(result_stub, &devices), "in device list")) {
         return;
     }
 
@@ -243,21 +243,26 @@ RichStatus WebUsbDevice::bulk_out_transfer(uint8_t ep_num, cbufptr_t buffer, Cal
     return RichStatus::success();
 }
 
-void WebUsbDevice::on_open_finished(const JsStub& stub) {
-    F_LOG_D(webusb_->logger_, "open finished");
-    open_cb_.invoke_and_clear(this);
+void WebUsbDevice::on_open_finished(const JsStub& result_stub, const JsStub& error_stub) {
+    if (error_stub.type != JsType::kUndefined) {
+        F_LOG_D(webusb_->logger_, "open failed with type " << (int)error_stub.type);
+        // TODO: error handling
+    } else {
+        F_LOG_D(webusb_->logger_, "open finished");
+        open_cb_.invoke_and_clear(this);
+    }
 }
 
-void WebUsbDevice::on_claim_interface_finished(const JsStub& stub) {
+void WebUsbDevice::on_claim_interface_finished(const JsStub& result_stub, const JsStub& error_stub) {
     F_LOG_D(webusb_->logger_, "claim_interface finished");
     claim_interface_cb_.invoke_and_clear(this);
 }
 
-void WebUsbDevice::on_bulk_in_transfer_finished(const JsStub& stub) {
+void WebUsbDevice::on_bulk_in_transfer_finished(const JsStub& result_stub, const JsStub& error_stub) {
     F_LOG_T(webusb_->logger_, "bulk_in_transfer finished");
 
     std::unordered_map<std::string, JsStub> result;
-    if (F_LOG_IF_ERR(webusb_->logger_, from_js(stub, &result), "can't parse transfer result")) {
+    if (F_LOG_IF_ERR(webusb_->logger_, from_js(result_stub, &result), "can't parse transfer result")) {
         return; // TODO: propagate error to callback
     }
 
@@ -296,11 +301,11 @@ void WebUsbDevice::on_bulk_in_transfer_finished(const JsStub& stub) {
     bulk_in_transfer_cb_.invoke_and_clear(RichStatus::success(), end);
 }
 
-void WebUsbDevice::on_bulk_out_transfer_finished(const JsStub& stub) {
+void WebUsbDevice::on_bulk_out_transfer_finished(const JsStub& result_stub, const JsStub& error_stub) {
     F_LOG_T(webusb_->logger_, "bulk_out_transfer finished");
 
     std::unordered_map<std::string, JsStub> result;
-    if (F_LOG_IF_ERR(webusb_->logger_, from_js(stub, &result), "can't parse transfer result")) {
+    if (F_LOG_IF_ERR(webusb_->logger_, from_js(result_stub, &result), "can't parse transfer result")) {
         return; // TODO: propagate error to callback
     }