diff --git a/README.md b/README.md
index fecac58..9ae468f 100644
--- a/README.md
+++ b/README.md
@@ -173,10 +173,15 @@ Generated spec:
 Generated TypeScript code: 
 
 ```typescript
-import { HubConnection, IStreamResult } from "@aspnet/signalr"
+import { HubConnection, IStreamResult } from '@aspnet/signalr';
 
 export class ChatHub {
+    private callbackForWelcome: () => void;
+    private callbackForSend: (message: string) => void;
+
     constructor(private connection: HubConnection) {
+        this.callbackForWelcome = undefined;
+        this.callbackForSend = undefined;
     }
 
     send(message: string): Promise<void> {
@@ -191,14 +196,24 @@ export class ChatHub {
         return this.connection.stream('GetEvents');
     }
 
-    registerCallbacks(implementation: IChatHubCallbacks) {
-        this.connection.on('Welcome', () => implementation.welcome());
-        this.connection.on('Send', (message) => implementation.send(message));
+    registerCallbacks(implementation: IChatHubCallbacks): void {
+        this.unregisterCallbacks();
+
+        this.callbackForWelcome = () => implementation.welcome();
+        this.connection.on('Welcome', this.callbackForWelcome);
+        this.callbackForSend = (message) => implementation.send(message);
+        this.connection.on('Send', this.callbackForSend);
     }
 
-    unregisterCallbacks(implementation: IChatHubCallbacks) {
-        this.connection.off('Welcome', () => implementation.welcome());
-        this.connection.off('Send', (message) => implementation.send(message));
+    unregisterCallbacks(): void {
+        if (this.callbackForWelcome !== undefined) {
+            this.connection.off('Welcome', this.callbackForWelcome);
+            this.callbackForWelcome = undefined;
+        }
+        if (this.callbackForSend !== undefined) {
+            this.connection.off('Send', this.callbackForSend);
+            this.callbackForSend = undefined;
+        }
     }
 }
 
diff --git a/src/HelloSignalR/Startup.cs b/src/HelloSignalR/Startup.cs
index f2a238e..b51e118 100644
--- a/src/HelloSignalR/Startup.cs
+++ b/src/HelloSignalR/Startup.cs
@@ -6,14 +6,29 @@ namespace HelloSignalR
 {
     public class Startup
     {
+        readonly string AllowAllPolicy = "AllowAllPolicy";
+
         public void ConfigureServices(IServiceCollection services)
         {
+            services.AddCors(options =>
+            {
+                options.AddPolicy(AllowAllPolicy,
+                    builder =>
+                    {
+                        builder
+                            .AllowAnyMethod()
+                            .AllowAnyHeader()
+                            .AllowAnyOrigin()
+                            .AllowCredentials();
+                    });
+            });
             services.AddSignalR();
         }
 
         public void Configure(IApplicationBuilder app, IHostingEnvironment env)
         {
             app.UseStaticFiles();
+            app.UseCors(AllowAllPolicy);
             app.UseSignalR(routes =>
             {
                 routes.MapHub<ChatHub>("/chat");
diff --git a/src/HelloSignalR/start_server.cmd b/src/HelloSignalR/start_server.cmd
new file mode 100644
index 0000000..84475b4
--- /dev/null
+++ b/src/HelloSignalR/start_server.cmd
@@ -0,0 +1,2 @@
+SET ASPNETCORE_URLS=http://localhost:61327
+dotnet run --no-launch-profile
\ No newline at end of file
diff --git a/src/SigSpec.CodeGeneration.TypeScript/Templates/File.liquid b/src/SigSpec.CodeGeneration.TypeScript/Templates/File.liquid
index de52ac1..96ca016 100644
--- a/src/SigSpec.CodeGeneration.TypeScript/Templates/File.liquid
+++ b/src/SigSpec.CodeGeneration.TypeScript/Templates/File.liquid
@@ -1,4 +1,4 @@
-import { HubConnection, IStreamResult } from "@microsoft/signalr"
+import { HubConnection, IStreamResult } from '@microsoft/signalr';
 {% for hub in Hubs -%}
 
 {{ hub }}
diff --git a/src/SigSpec.CodeGeneration.TypeScript/Templates/Hub.liquid b/src/SigSpec.CodeGeneration.TypeScript/Templates/Hub.liquid
index c5f8c74..6de943a 100644
--- a/src/SigSpec.CodeGeneration.TypeScript/Templates/Hub.liquid
+++ b/src/SigSpec.CodeGeneration.TypeScript/Templates/Hub.liquid
@@ -1,5 +1,12 @@
 export class {{ Name }}Hub {
+{% for operation in Callbacks -%}
+    private callbackFor{{ operation.Name }}: ({% for parameter in operation.Parameters %}{{ parameter.Name }}: {{ parameter.Type }}{% if forloop.last == false %}, {% endif %}{% endfor %}) => void;
+{% endfor -%}
+
     constructor(private connection: HubConnection) {
+{% for operation in Callbacks -%}
+        this.callbackFor{{ operation.Name }} = undefined;
+{% endfor -%}
     }
 {% for operation in Operations -%}
 
@@ -18,15 +25,21 @@
 {%     endif -%}
 {% endfor -%}
 
-    registerCallbacks(implementation: I{{ Name }}HubCallbacks) {
+    registerCallbacks(implementation: I{{ Name }}HubCallbacks): void {
+        this.unregisterCallbacks();
+
 {% for operation in Callbacks -%}
-        this.connection.on('{{ operation.Name }}', ({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %}) => implementation.{{operation.MethodName}}({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %}));
+        this.callbackFor{{ operation.Name }} = ({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %}) => implementation.{{operation.MethodName}}({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %});
+        this.connection.on('{{ operation.Name }}', this.callbackFor{{ operation.Name }});
 {% endfor -%}
     }
 
-    unregisterCallbacks(implementation: I{{ Name }}HubCallbacks) {
+    unregisterCallbacks(): void {
 {% for operation in Callbacks -%}
-        this.connection.off('{{ operation.Name }}', ({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %}) => implementation.{{operation.MethodName}}({% for parameter in operation.Parameters %}{{ parameter.Name }}{% if forloop.last == false %}, {% endif %}{% endfor %}));
+        if (this.callbackFor{{ operation.Name }} !== undefined) {
+            this.connection.off('{{ operation.Name }}', this.callbackFor{{ operation.Name }});
+            this.callbackFor{{ operation.Name }} = undefined;
+        }
 {% endfor -%}
     }
 }