Dev Mode in Visual Studio

Dev Mode is a new feature for TypeScript 1.4 and higher that allows you to

1. Use a custom language service file of your choosing.
2. Debug the script side of the language service Visual Studio is using during a session.

Enabling Dev Mode

In Visual Studio 2013

1. Open up the Registry Editor (regedit.exe from the Run prompt).
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\12.0\TypeScriptLanguageService (or create the key if it does not exist).
3. Create a new DWORD (32-bit) Value with the name EnableDevMode.
4. Right click the EnableDevMode value and Modify it.
5. Change the Value data to 1.

In Visual Studio 2015

1. Open up the Registry Editor (regedit.exe from the Run prompt).
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\14.0\TypeScriptLanguageService (or create the key if it does not exist).
3. Create a new DWORD (32-bit) Value with the name EnableDevMode.
4. Right click the EnableDevMode value and Modify it.
5. Change the value data to 1.

Using a custom language service file

1. Enable dev mode.
2. Open up the Registry Editor.
3. Navigate to the applicable TypeScriptLanguageService key.

• In Visual Studio 2013: HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\12.0\TypeScriptLanguageService
• In Visual Studio 2015: HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\14.0\TypeScriptLanguageService

4. Create a new String Value with the name CustomTypeScriptServicesFileLocation.
5. Right click the CustomTypeScriptServicesFileLocation value and Modify it.
6. Change the value data to the full path of your alternative services file (e.g. C:\Users\drosen\TypeScript\built\local\typescriptServices.js)

Hot swapping

When the language service's script side is modified in any way (whether or not you are using a custom location for your language service file), it will be reloaded on the fly. This means you should see changes instantaneously. However, this means that when debugging, your language service threads will be purged.

Debugging the language service in Visual Studio using Visual Studio

1. Have a running instance of Visual Studio 2013/2015 with an open TypeScript file.
2. Open a new instance of Visual Studio 2013/2015.
3. Bring up the Attach to Process dialog by either

• Using menu bar and navigating from Debug -> Attach to Process.
• Clicking on the Attach button from the Standard toolbar if it is visible.

4. In the row labeled Attach to:, click on the Select... button.
5. Click the radio button Debug these code types and select Script. Then press OK.
6. Find the appropriate Visual Studio instance in your list. Visual Studio instances have the process name devenv.exe and you can typically narrow down your instance looking for its current file in the Title field.
7. Hit the Attach button. In the Solution Exporer. you should now see four active debuggers (one for each language service thread).

At this point you should be able to hit debug points and get an understanding of what's going on.

Language Service Threads

• Classifier_N: This thread runs the lexical classifier - a line-oriented classifier which is primarily concerned with fast rudimentary colorization.
• CoreServices_N: This is used to calculate the virtual project space in VS, and needs more documentation.
• LanguageService_N and LanguageService_N: Unfortunately these haven't been distinctly named.
  • One of these is the syntactic classifier, giving accurate (semantically agnostic) classifications.
  • The other needs to be documented more thoroughly.