The thought of using JavaScript and HTML to create a Metro style application sounds great, but many developers have rightly expressed concern that JavaScript just isn’t suitable for tasks such as advanced 3D graphics and video processing. Microsoft’s solution to that problem is to combine JavaScript with C++.
By using JavaScript for the creation of the User Interface (UI) and other, more simple aspects of the app, and saving C++ for the more hardcore, technical aspects of the app, developers will be able to create compelling apps which look, feel and act no different than other applications that were created using more traditional programming languages.