Visual Studio 2012: Convert an existing ASP.NET Web project to be able to compile TypeScript

Problem:
You add TypeScript file to an existing Visual Studio web project, but when you build the project, the TypeScript files do not generate equivalent JavaScript file.

Assumptions:
- you have installed the TypeScript plugin for Visual Studio 2012/2013
- when you right-click on the TypeScript file and select Properties, the BuildAction is set to be TypeScripCompile.

Solution:
In Visual Studio 2012: in order to use TypeScript files in an existing ASP.NET Web project, you need to make a manual change to the project file.

you need to:

1. right click on the project, select Unload Project.
1. right click on the project, select Edit.

Scroll down the XML file, to the end tag:

 </Project>  

just before the end tag, insert this XML:

  <PropertyGroup Condition="'$(Configuration)' == 'Debug'">  
   <TypeScriptTarget>ES3</TypeScriptTarget>  
   <TypeScriptRemoveComments>false</TypeScriptRemoveComments>  
   <TypeScriptSourceMap>true</TypeScriptSourceMap>  
   <TypeScriptModuleKind>AMD</TypeScriptModuleKind>  
  </PropertyGroup>  
  <PropertyGroup Condition="'$(Configuration)' == 'Release'">  
   <TypeScriptTarget>ES3</TypeScriptTarget>  
   <TypeScriptRemoveComments>true</TypeScriptRemoveComments>  
   <TypeScriptSourceMap>false</TypeScriptSourceMap>  
   <TypeScriptModuleKind>AMD</TypeScriptModuleKind>  
  </PropertyGroup>  
  <Import Project="$(VSToolsPath)\TypeScript\Microsoft.TypeScript.targets" />  
 </Project>  

note: if you want to use newer JavaScript features such as properties, then you need ECMAScript 5 support (and a newer browser such as IE9 and up), and so you need to replace ES3 with ES5 in the above text.
This resolves this compile error:
Accessors are only available when targeting ECMAScript 5 and higher.

Save your changes.
Right-click on the project, select Reload Project.

Build the project.

The TypeScript files should now compile OK, and output equivalent JavaScript files.