If you create an ExtJS Workspace or Application (universal) using Visual Studio 2015 . Running the solution will automatically cause an exception when launching the ExtJS App because Ext wants to load classic.json but cannot because it is blocked by IIS.

Failed to load resource: the server responded with a status of 404 (Not Found), http://localhost:7219/ExtApp1/classic.json?_dc=1475610724389
Solution is to add the following to the web config, but I would expect create new workspace/application would automatically enable this in the web.config since the app won't work otherwise:

<?xml version="1.0"?>
      <mimeMap fileExtension=".json" mimeType="application/json" />