diff --git a/index.html b/index.html
index 3335c08..7e960f7 100644
--- a/index.html
+++ b/index.html
@@ -285,6 +285,9 @@
 <script type="text/javascript" src="libs/jquery-1.11.2.min.js"></script>
 <script type="text/javascript" src="libs/underscore-min.js" async></script>
 <script type="text/javascript" src="libs/ZeroClipboard.min.js" async></script>
+<script type="text/javascript" src="scratch_extensions/scratch_proxies.js" defer></script>
+<script type="text/javascript" src="scratch_extensions/scratch_plugin.js" defer></script>
+<script type="text/javascript" src="scratch_extensions/scratch_nmh.js" defer></script>
 <script type="text/javascript" src="scratch_extensions/scratch_ext.js" defer></script>
 <script type="text/javascript" src="js/scratchx.js" defer></script>
 </body>
diff --git a/scratch_extensions/scratch_ext.js b/scratch_extensions/scratch_ext.js
index b9dd563..517e196 100644
--- a/scratch_extensions/scratch_ext.js
+++ b/scratch_extensions/scratch_ext.js
@@ -4,9 +4,7 @@
 //
 // Scratch 2.0 extension manager which Scratch communicates with to initialize extensions and communicate with them.
 // The extension manager also handles creating the browser plugin to enable access to HID and serial devices.
-window.ScratchExtensions = new (function(){
-    var pluginName = 'Scratch Device Plugin'; // will be 'Scratch Plugin for Devices'
-    var pluginAvailable = (window.ActiveXObject || !!navigator.plugins[pluginName]) && !!window.ArrayBuffer;
+window.ScratchExtensions = new (function () {
     var plugin = null;
     var handlers = {};
     var blockDefs = {};
@@ -16,27 +14,34 @@ window.ScratchExtensions = new (function(){
     var poller = null;
     var lib = this;
 
-    lib.register = function(name, descriptor, handler, deviceSpec) {
-        if(name in handlers) {
-            console.log('Scratch extension "'+name+'" already exists!');
+    var isOffline = (Scratch && Scratch.FlashApp && Scratch.FlashApp.ASobj &&
+            Scratch.FlashApp.ASobj.isOffline && Scratch.FlashApp.ASobj.isOffline());
+    var pluginAvailable = function () {
+        return !!window.ArrayBuffer && !!(
+                isOffline ||
+                (window.ScratchPlugin && window.ScratchPlugin.isAvailable()) ||
+                (window.ScratchDeviceHost && window.ScratchDeviceHost.isAvailable())
+            );
+    };
+
+    lib.register = function (name, descriptor, handler, deviceSpec) {
+        if (name in handlers) {
+            console.log('Scratch extension "' + name + '" already exists!');
             return false;
         }
 
-        if(deviceSpec) {
-            if(!pluginAvailable && window.ActiveXObject) {
+        if (deviceSpec && !plugin) {
+            if (pluginAvailable()) {
+                setTimeout(createDevicePlugin, 10);
+            } else if (window.ScratchPlugin.useActiveX) {
                 JSsetProjectBanner('Sorry, your version of Internet Explorer is not supported.  Please upgrade to version 10 or 11.');
             }
-            if(pluginAvailable && !plugin) setTimeout(createDevicePlugin, 10);
-
-            // Wait a moment to access the plugin and claim any devices that plugins are
-            // interested in.
-            setTimeout(checkPolling, 100);
         }
 
         handlers[name] = handler;
         blockDefs[name] = descriptor.blocks;
-        if(descriptor.menus) menuDefs[name] = descriptor.menus;
-        if(deviceSpec) deviceSpecs[name] = deviceSpec;
+        if (descriptor.menus) menuDefs[name] = descriptor.menus;
+        if (deviceSpec) deviceSpecs[name] = deviceSpec;
 
         // Show the blocks in Scratch!
         var extObj = {
@@ -51,81 +56,86 @@ window.ScratchExtensions = new (function(){
     };
 
     var loadingURL;
-    lib.loadExternalJS = function(url) {
+    lib.loadExternalJS = function (url) {
         var scr = document.createElement("script");
         scr.src = url;// + "?ts=" + new Date().getTime();
         loadingURL = url;
         document.getElementsByTagName("head")[0].appendChild(scr);
     };
 
-    lib.loadLocalJS = function(code) {
+    lib.loadLocalJS = function (code) {
         // Run the extension code in the global scope
         try {
             (new Function(code))();
-        } catch(e) {
+        } catch (e) {
             console.log(e.stack.toString());
         }
     };
 
-    lib.unregister = function(name) {
-        try { handlers[name]._shutdown(); } catch(e){}
+    lib.unregister = function (name) {
+        try { handlers[name]._shutdown(); } catch (e) { }
         delete handlers[name];
         delete blockDefs[name];
         delete menuDefs[name];
         delete deviceSpecs[name];
     };
 
-    lib.canAccessDevices = function() { return pluginAvailable; };
-    lib.getReporter = function(ext_name, reporter, args) {
+    lib.canAccessDevices = function () { return pluginAvailable(); };
+    lib.getReporter = function (ext_name, reporter, args) {
         return handlers[ext_name][reporter].apply(handlers[ext_name], args);
     };
 
-    lib.getReporterAsync = function(ext_name, reporter, args, job_id) {
-        var callback = function(retval) {
+    lib.getReporterAsync = function (ext_name, reporter, args, job_id) {
+        var callback = function (retval) {
             Scratch.FlashApp.ASobj.ASextensionReporterDone(ext_name, job_id, retval);
         }
         args.push(callback);
         handlers[ext_name][reporter].apply(handlers[ext_name], args);
     };
 
-    lib.runCommand = function(ext_name, command, args) {
+    lib.getReporterForceAsync = function (ext_name, reporter, args, job_id) {
+        var retval = handlers[ext_name][reporter].apply(handlers[ext_name], args);
+        Scratch.FlashApp.ASobj.ASextensionReporterDone(ext_name, job_id, retval);
+    };
+
+    lib.runCommand = function (ext_name, command, args) {
         handlers[ext_name][command].apply(handlers[ext_name], args);
     };
 
-    lib.runAsync = function(ext_name, command, args, job_id) {
-        var callback = function() {
+    lib.runAsync = function (ext_name, command, args, job_id) {
+        var callback = function () {
             Scratch.FlashApp.ASobj.ASextensionCallDone(ext_name, job_id);
         }
         args.push(callback);
         handlers[ext_name][command].apply(handlers[ext_name], args);
     };
 
-    lib.getStatus = function(ext_name) {
-        if(!(ext_name in handlers))
-            return {status: 0, msg: 'Not loaded'};
+    lib.getStatus = function (ext_name) {
+        if (!(ext_name in handlers))
+            return { status: 0, msg: 'Not loaded' };
 
-        if(ext_name in deviceSpecs && !pluginAvailable)
-            return {status: 0, msg: 'Missing browser plugin'};
+        if (ext_name in deviceSpecs && !pluginAvailable())
+            return { status: 0, msg: 'Missing browser plugin' };
 
         return handlers[ext_name]._getStatus();
     };
 
-    lib.notify = function(text) {
-        if(window.JSsetProjectBanner) JSsetProjectBanner(text);
+    lib.notify = function (text) {
+        if (window.JSsetProjectBanner) JSsetProjectBanner(text);
         else alert(text);
     };
 
-    lib.resetPlugin = function() {
+    lib.resetPlugin = function () {
         if (plugin && plugin.reset) plugin.reset();
         shutdown();
     };
 
-    $(window).unload(function(e) {
+    $(window).unload(function (e) {
         shutdown();
     });
 
     function shutdown() {
-        for(var extName in handlers)
+        for (var extName in handlers)
             handlers[extName]._shutdown();
         handlers = {};
         stopPolling();
@@ -133,65 +143,88 @@ window.ScratchExtensions = new (function(){
 
     function checkDevices() {
         var awaitingSpecs = {};
-        for(var ext_name in deviceSpecs)
-            if(!devices[ext_name]) {
+        for (var ext_name in deviceSpecs)
+            if (!devices[ext_name]) {
                 var spec = deviceSpecs[ext_name];
-                if(spec.type == 'hid') {
-                    if(!awaitingSpecs['hid']) awaitingSpecs['hid'] = {};
+                if (spec.type == 'hid') {
+                    if (!awaitingSpecs['hid']) awaitingSpecs['hid'] = {};
                     awaitingSpecs['hid'][spec.vendor + '_' + spec.product] = ext_name;
                 }
-                else if(spec.type == 'serial')
+                else if (spec.type == 'serial')
                     awaitingSpecs['serial'] = ext_name;
             }
 
-        if(awaitingSpecs['hid']) {
-            var deviceList = plugin.hid_list();
-            var hidList = awaitingSpecs['hid'];
-            for (var i = 0; i < deviceList.length; i++) {
-                var ext_name = hidList[deviceList[i]["vendor_id"] + '_' + deviceList[i]["product_id"]];
-                if (ext_name)
-                    handlers[ext_name]._deviceConnected(new hidDevice(deviceList[i], ext_name));
-            }
+        if (awaitingSpecs['hid']) {
+            plugin.hid_list(function (deviceList) {
+                var hidList = awaitingSpecs['hid'];
+                for (var i = 0; i < deviceList.length; i++) {
+                    var ext_name = hidList[deviceList[i]["vendor_id"] + '_' + deviceList[i]["product_id"]];
+                    if (ext_name)
+                        handlers[ext_name]._deviceConnected(new hidDevice(deviceList[i], ext_name));
+                }
+            });
         }
 
-        if(awaitingSpecs['serial']) {
+        if (awaitingSpecs['serial']) {
             var ext_name = awaitingSpecs['serial'];
-            var deviceList = plugin.serial_list();
-            for (var i = 0; i < deviceList.length; i++) {
-                handlers[ext_name]._deviceConnected(new serialDevice(deviceList[i], ext_name));
-            }
+            plugin.serial_list(function (deviceList) {
+                for (var i = 0; i < deviceList.length; i++) {
+                    handlers[ext_name]._deviceConnected(new serialDevice(deviceList[i], ext_name));
+                }
+            });
         }
 
-        if(!shouldLookForDevices())
+        if (!shouldLookForDevices())
             stopPolling();
     }
 
     function checkPolling() {
-        if(poller || !shouldLookForDevices()) return;
+        if (poller || !shouldLookForDevices()) return;
 
         poller = setInterval(checkDevices, 500);
-   }
+    }
 
     function stopPolling() {
-        if(poller) clearInterval(poller);
+        if (poller) clearInterval(poller);
         poller = null;
     }
 
     function shouldLookForDevices() {
-        for(var ext_name in deviceSpecs)
-            if(!devices[ext_name])
+        for (var ext_name in deviceSpecs)
+            if (!devices[ext_name])
                 return true;
 
         return false;
     }
 
     function createDevicePlugin() {
-        if(plugin) return;
+        if (plugin) return;
 
-        var pluginContainer = document.createElement('div');
-        document.getElementById('scratch').parentNode.appendChild(pluginContainer);
-        pluginContainer.innerHTML = '<object type="application/x-scratchdeviceplugin" width="1" height="1" codebase="/scratchr2/static/ext/ScratchDevicePlugin.cab"> </object>';
-        plugin = pluginContainer.firstChild;
+        // TODO: delegate more of this to the other files
+        if (isOffline) {
+            // Talk to the AIR Native Extension through the offline editor's plugin emulation.
+            plugin = Scratch.FlashApp.ASobj.getPlugin();
+        } else if (window.ScratchDeviceHost && window.ScratchDeviceHost.isAvailable()) {
+            // Talk to the Native Messaging Host through a Chrome extension.
+            plugin = window.ScratchDeviceHost;
+        } else {
+            if (window.ScratchPlugin.useActiveX) {
+                // we must be on IE or similar
+                plugin = new ActiveXObject(window.ScratchPlugin.axObjectName);
+            } else {
+                // Not IE: try NPAPI
+                var pluginContainer = document.createElement('div');
+                document.getElementById('scratch').parentNode.appendChild(pluginContainer);
+                pluginContainer.innerHTML = '<object type="application/x-scratchdeviceplugin" width="1" height="1"> </object>';
+                plugin = pluginContainer.firstChild;
+            }
+            // Talk to the actual plugin, but make it pretend to be asynchronous.
+            plugin = new window.ScratchPlugin.PluginWrapper(plugin);
+        }
+
+        // Wait a moment to access the plugin and claim any devices that plugins are
+        // interested in.
+        setTimeout(checkPolling, 100);
     }
 
     function hidDevice(info, ext_name) {
@@ -205,44 +238,47 @@ window.ScratchExtensions = new (function(){
         this.info = info;
 
         function disconnect() {
-            setTimeout(function(){
+            setTimeout(function () {
                 self.close();
                 handlers[ext_name]._deviceRemoved(self);
             }, 0);
         }
 
-        this.open = function() {
+        this.open = function (readyCallback) {
             try {
-                dev = plugin.hid_open(this.id);
-                if(window.ActiveXObject) dev = dev(this.id);
-                dev.set_nonblocking(true);
-                //devices[ext_name][path] = this;
-                devices[ext_name] = this;
+                plugin.hid_open(this.id, function (d) {
+                    dev = d;
+                    dev.set_nonblocking(true);
+                    //devices[ext_name][path] = this;
+                    devices[ext_name] = this;
+
+                    if (readyCallback) readyCallback(this);
+                });
             }
-            catch(e) {}
+            catch (e) { }
         };
-        this.close = function() {
-            if(!dev) return;
+        this.close = function () {
+            if (!dev) return;
             dev.close();
             delete devices[ext_name];
             dev = null;
 
             checkPolling();
         };
-        this.write = function(data) {
-            if(!dev) return;
-            var len = dev.write(data);
-            if(window.ActiveXObject) len = len(data);
-            if(len < 0) disconnect();
-            return len;
+        this.write = function (data, callback) {
+            if (!dev) return;
+            dev.write(data, function (len) {
+                if (len < 0) disconnect();
+                if (callback) callback(len);
+            });
         };
-        this.read = function(len) {
-            if(!dev) return null;
-            if(!len) len = 65;
-            var data = dev.read(len);
-            if(window.ActiveXObject) data = data(len);
-            if(data.byteLength == 0) disconnect();
-            return data;
+        this.read = function (callback, len) {
+            if (!dev) return null;
+            if (!len) len = 65;
+            dev.read(len, function (data) {
+                if (data.byteLength == 0) disconnect();
+                callback(data);
+            });
         };
     }
 
@@ -254,32 +290,42 @@ window.ScratchExtensions = new (function(){
         //if(!(ext_name in devices)) devices[ext_name] = {};
 
         this.id = id;
-        this.open = function(opts) {
+        this.open = function (opts, readyCallback) {
             try {
-                dev = plugin.serial_open(this.id, opts);
-//                dev.set_disconnect_handler(function() {
-//                    self.close();
-//                    handlers[ext_name]._deviceRemoved(self);
-//                });
-                //devices[ext_name][path] = this;
-                devices[ext_name] = this;
+                plugin.serial_open(this.id, opts, function (d) {
+//                    dev.set_disconnect_handler(function () {
+//                        self.close();
+//                        handlers[ext_name]._deviceRemoved(self);
+//                    });
+//                    devices[ext_name][path] = this;
+                    dev = d;
+                    devices[ext_name] = this;
+
+                    dev.set_error_handler(function (message) {
+                        alert('Serial device error\n\nDevice: ' + id + '\nError: ' + message);
+                    });
+
+                    if (readyCallback) readyCallback(this);
+                });
+            }
+            catch (e) {
+                console.log('Error opening serial device ' + id + ': ' + e);
             }
-            catch(e) {}
         };
-        this.close = function() {
-            if(!dev) return;
+        this.close = function () {
+            if (!dev) return;
             dev.close();
             delete devices[ext_name];
             dev = null;
 
             checkPolling();
         };
-        this.send = function(data) {
-            if(!dev) return;
+        this.send = function (data) {
+            if (!dev) return;
             dev.send(data);
         };
-        this.set_receive_handler = function(handler) {
-            if(!dev) return;
+        this.set_receive_handler = function (handler) {
+            if (!dev) return;
             dev.set_receive_handler(handler);
         };
     }
diff --git a/scratch_extensions/scratch_nmh.js b/scratch_extensions/scratch_nmh.js
new file mode 100644
index 0000000..08067fb
--- /dev/null
+++ b/scratch_extensions/scratch_nmh.js
@@ -0,0 +1,184 @@
+// Communicate with the Scratch Native Messaging Host through an extension.
+window.ScratchDeviceHost = new (function () {
+    var self = this;
+    var isConnected = false;
+
+    self.isAvailable = function () {
+        return isConnected;
+    };
+
+    if (!window.chrome) return;
+
+    var extensionID = 'clmabinlolakdafkoajkfjjengcdmnpm';
+    var callNumber = 0;
+    var port = chrome.runtime.connect(extensionID);
+    console.assert(port, "Failed to create port");
+
+    var messageHandlers = {};
+    port.onMessage.addListener(function (message) {
+        var messageName = message[0];
+        if (messageName == "@") {
+            var callbackToken = message[1];
+            var returnValue = message[2];
+            var callback = pendingCallbacks[callbackToken];
+            delete pendingCallbacks[callbackToken];
+            if (callback) callback(returnValue);
+        } else {
+            var handler = messageHandlers[messageName];
+            if (handler) {
+                handler(message);
+            } else {
+                console.log("SDH-Page: Unrecognized message " + message);
+            }
+        }
+    });
+
+    messageHandlers["serialRecv"] = function (message) {
+        var path = message[1];
+        var data = message[2];
+
+        var device = serialDevices[path];
+        if (device && device.receiveHandler) {
+            device.receiveHandler(data);
+        }
+    };
+
+    messageHandlers["serialError"] = function (message) {
+        var path = message[1];
+        var errorMessage = message[2];
+
+        var device = serialDevices[path];
+        if (device && device.errorHandler) {
+            device.errorHandler(errorMessage);
+        }
+    };
+
+    var pendingCallbacks = {};
+    function sendMessage(message, callback) {
+        var callbackToken = (callNumber++).toString();
+        pendingCallbacks[callbackToken] = callback;
+        port.postMessage([callbackToken, message]);
+    }
+
+    sendMessage(["version"], function (version) {
+        isConnected = true;
+    });
+
+    self.hid_list = function (callback, opt_vendorID, opt_productID) {
+        var message = ["hid_list", opt_vendorID || 0, opt_productID || 0];
+        sendMessage(message, function (deviceList) {
+            if (callback) callback(deviceList);
+        });
+    };
+    self.hid_open = function (path, callback) {
+        var message = ["hid_open_raw", path];
+        sendMessage(message, function (result) {
+            var device;
+            if (result) {
+                device = new HidDevice(path);
+                ScratchProxies.AddHidProxies(device);
+                var claimMessage = ["claim", path];
+                sendMessage(claimMessage);
+            }
+            if (callback) callback(device);
+        });
+    };
+    self.serial_list = function (callback) {
+        sendMessage(["serial_list"], function (deviceList) {
+            if (callback) callback(deviceList);
+        });
+    };
+    self.serial_open = function (path, opts, callback) {
+        var message = ["serial_open_raw", path];
+        if (opts) message.push(opts);
+        sendMessage(message, function (result) {
+            var device;
+            if (result) {
+                device = new SerialDevice(path);
+                ScratchProxies.AddSerialProxies(device);
+                var claimMessage = ["claim", path];
+                sendMessage(claimMessage);
+            }
+            if (callback) callback(device);
+        });
+    };
+    self.reset = function () {
+        sendMessage(["reset"]);
+    };
+    self.version = function (callback) {
+        sendMessage(["version"], function (result) {
+            if (callback) callback(result);
+        });
+    };
+
+    function HidDevice(path) {
+        var self = this;
+
+        self.write_raw = function (arrayBuffer, callback) {
+            var message = ["write_raw", path, arrayBuffer];
+            sendMessage(message, function (result) {
+                if (callback) callback(result);
+            });
+        };
+        self.send_feature_report_raw = function (arrayBuffer, callback) {
+            var message = ["send_feature_report_raw", path, arrayBuffer];
+            sendMessage(message, function (result) {
+                if (callback) callback(result);
+            });
+        };
+        self.read_raw = function (size, callback) {
+            var message = ["read_raw", path, size];
+            sendMessage(message, function (data) {
+                if (callback) callback(data);
+            });
+        };
+        self.get_feature_report_raw = function (size, callback) {
+            var message = ["get_feature_report_raw", path, size];
+            sendMessage(message, function (data) {
+                if (callback) callback(data);
+            });
+        };
+        self.set_nonblocking = function (flag, callback) {
+            var message = ["set_nonblocking", path, flag];
+            sendMessage(message, function (result) {
+                if (callback) callback(result);
+            });
+        };
+        self.close = function () {
+            sendMessage(["close", path]);
+        };
+    }
+
+    var serialDevices = {}; // path -> SerialDevice
+    function SerialDevice(path) {
+        var self = this;
+
+        self.receiveHandler = undefined;
+        self.errorHandler = undefined;
+
+        serialDevices[path] = self;
+
+        self.send_raw = function (data) {
+            var message = ["serial_send_raw", path, data];
+            sendMessage(message);
+        };
+        self.close = function () {
+            var message = ["serial_close", path];
+            sendMessage(message);
+        };
+        self.is_open = function (callback) {
+            var message = ["serial_is_open", path];
+            sendMessage(message, function (result) {
+                if (callback) callback(result);
+            });
+        };
+        self.set_receive_handler_raw = function (callback) {
+            self.receiveHandler = callback;
+            var message = ["serial_recv_start", path];
+            sendMessage(message);
+        };
+        self.set_error_handler = function (callback) {
+            self.errorHandler = callback;
+        };
+    }
+})();
diff --git a/scratch_extensions/scratch_plugin.js b/scratch_extensions/scratch_plugin.js
new file mode 100644
index 0000000..3912bbf
--- /dev/null
+++ b/scratch_extensions/scratch_plugin.js
@@ -0,0 +1,96 @@
+window.ScratchPlugin = new (function () {
+    var self = this;
+
+    var pluginName = 'Scratch Device Plugin'; // will be 'Scratch Plugin for Devices'
+    self.useActiveX = window.hasOwnProperty('ActiveXObject');
+    self.axObjectName = 'MITMediaLab.ScratchDevicePlugin'; // name of ActiveX object
+    self.isAvailable = function () {
+        return !!(self.useActiveX || navigator.plugins[pluginName]);
+    };
+
+    // These wrappers make the plugin act asynchronous, matching the API found in AIR and NMH.
+    // The one difference is that callbacks are triggered before the initiating call returns.
+    self.PluginWrapper = function (plugin) {
+        var self = this;
+        self.hid_list = function (callback, opt_vendorID, opt_productID) {
+            var deviceList = plugin.hid_list(opt_vendorID, opt_productID);
+            if (callback) callback(deviceList);
+        };
+        self.hid_open = function (path, callback) {
+            var device = plugin.hid_open_raw(path);
+            if (device) {
+                device = new HidWrapper(device);
+                ScratchProxies.AddHidProxies(device);
+            }
+            if (callback) callback(device);
+        };
+        self.serial_list = function (callback) {
+            var deviceList = plugin.serial_list();
+            if (callback) callback(deviceList);
+        };
+        self.serial_open = function (path, opts, callback) {
+            var device = plugin.serial_open_raw(path, opts);
+            if (device) {
+                device = new SerialWrapper(device);
+                ScratchProxies.AddSerialProxies(device);
+            }
+            if (callback) callback(device);
+        };
+        self.reset = function () {
+            plugin.reset();
+        };
+        self.version = function (callback) {
+            var result = plugin.version();
+            if (callback) callback(result);
+        };
+    };
+
+    function HidWrapper(device) {
+        var self = this;
+
+        self.write_raw = function (arrayBuffer, callback) {
+            var result = device.write_raw(arrayBuffer);
+            if (callback) callback(result);
+        };
+        self.send_feature_report_raw = function (arrayBuffer, callback) {
+            var result = device.send_feature_report_raw(arrayBuffer);
+            if (callback) callback(result);
+        };
+        self.read_raw = function (size, callback) {
+            var data = device.read_raw(size);
+            if (callback) callback(data);
+        };
+        self.get_feature_report_raw = function (size, callback) {
+            var data = device.get_feature_report_raw(size);
+            if (callback) callback(data);
+        };
+        self.set_nonblocking = function (flag, callback) {
+            var result = device.set_nonblocking(flag);
+            if (callback) callback(result);
+        };
+        self.close = function () {
+            device.close();
+        };
+    };
+
+    function SerialWrapper(device) {
+        var self = this;
+
+        self.send_raw = function (data) {
+            device.send_raw(data);
+        };
+        self.close = function () {
+            device.close();
+        };
+        self.is_open = function (callback) {
+            var result = device.is_open();
+            if (callback) callback(result);
+        };
+        self.set_receive_handler_raw = function (callback) {
+            device.set_receive_handler_raw(callback);
+        };
+        self.set_error_handler = function (callback) {
+            device.set_error_handler(callback);
+        };
+    };
+})();
diff --git a/scratch_extensions/scratch_proxies.js b/scratch_extensions/scratch_proxies.js
new file mode 100644
index 0000000..a11b782
--- /dev/null
+++ b/scratch_extensions/scratch_proxies.js
@@ -0,0 +1,91 @@
+// Extend hardware devices with some hardware-API-agnostic data conversion wrappers
+window.ScratchProxies = new (function () {
+    var self = this;
+    var charsBase64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+
+    function ab_to_b64(arraybuffer) {
+        var bytes = new Uint8Array(arraybuffer), i, len = bytes.length, base64 = '';
+
+        for (i = 0; i < len; i += 3) {
+            base64 += charsBase64[bytes[i] >> 2];
+            base64 += charsBase64[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
+            base64 += charsBase64[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
+            base64 += charsBase64[bytes[i + 2] & 63];
+        }
+
+        if ((len % 3) === 2) {
+            base64 = base64.substring(0, base64.length - 1) + '=';
+        } else if (len % 3 === 1) {
+            base64 = base64.substring(0, base64.length - 2) + '==';
+        }
+
+        return base64;
+    }
+
+    function b64_to_ab(base64) {
+        var bufferLength = base64.length * 0.75, len = base64.length, i, p = 0, encoded1, encoded2, encoded3, encoded4;
+        if (base64[base64.length - 1] === '=') {
+            --bufferLength;
+            if (base64[base64.length - 2] === '=') {
+                --bufferLength;
+            }
+        }
+
+        var arraybuffer = new ArrayBuffer(bufferLength), bytes = new Uint8Array(arraybuffer);
+        for (i = 0; i < len; i += 4) {
+            encoded1 = charsBase64.indexOf(base64[i]);
+            encoded2 = charsBase64.indexOf(base64[i + 1]);
+            encoded3 = charsBase64.indexOf(base64[i + 2]);
+            encoded4 = charsBase64.indexOf(base64[i + 3]);
+            bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
+            bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
+            bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
+        }
+
+        return arraybuffer;
+    }
+
+    self.AddHidProxies = function (device) {
+        device.write = function (arrayBuffer, callback) {
+            var bufferBase64 = ab_to_b64(arrayBuffer);
+            device.write_raw(bufferBase64, callback);
+        };
+        device.send_feature_report = function (arrayBuffer, callback) {
+            var bufferBase64 = ab_to_b64(arrayBuffer);
+            device.send_feature_report_raw(bufferBase64, callback);
+        };
+        device.read = function (size, callback) {
+            device.read_raw(size, function (data) {
+                if (callback) {
+                    data = b64_to_ab(data);
+                    callback(data);
+                }
+            });
+        };
+        device.get_feature_report = function (size, callback) {
+            device.get_feature_report_raw(size, function (data) {
+                if (callback) {
+                    data = b64_to_ab(data);
+                    callback(data);
+                }
+            });
+        };
+    };
+
+    self.AddSerialProxies = function (device) {
+        device.send = function (arrayBuffer, callback) {
+            var bufferBase64 = ab_to_b64(arrayBuffer);
+            device.send_raw(bufferBase64, function (result) {
+                if (callback) callback(result);
+            });
+        };
+        device.set_receive_handler = function (callback) {
+            device.set_receive_handler_raw(function (data) {
+                if (callback) {
+                    data = b64_to_ab(data);
+                    callback(data);
+                }
+            });
+        };
+    };
+})();