One of the best examples of how Microsoft is extending the range of controls that you can access from JavaScript and HTML is the app bar. It also happens to be a very useful standard UI element.

The Template object is useful in its own right, but add it to data binding and you have a easy-to-use way to present data to the user.  It also happens to be the easiest way to find out about data binding in general.

One of the most noticeable features of WinRT/Metro is the use of tiles. At the simplest level, a tile acts as little more than an icon for your app. Taken just a little further, however, and a live tile can be used communicate with the user. Exactly how all of this works can be a bit confusing, so let's find out about its fundamental principles.

Live tiles are a big plus if you are designing for Metro/WinRT and, as long as you understand how it all works, it isn't difficult to implement updates.

Metro doesn't allow you very many ways to interact with the user when your app wants to, so you need to master the few at your disposal - toast popups in particular. Fortunately they aren't difficult and follow the same pattern as the other notifications - badges, and tiles.

We have looked at WinJS controls and how to make use of them, but what do you do when the control you need doesn't exist? One solution is to create a custom control. As most of WinJS is just simple JavaScript with very little added, this is easier than you might expect.

WinRT is mostly an asynchronous system and making the best of this is a matter of using the promise object. The promise object makes asynchronous code easy to use and easier to create. Promises are a proposed JavaScript standard.

If you want to keep the user interface fast and responsive you have to follow the framework and create asynchronous functions - but how? This sounds complicated. The solution is to make use of Web Workers and wrap what you create so that it returns a promise. Let's see how it all fits together.