When building an app using a library for the platform, it is important to understand the features that the library provides. In this chapter, you’ll look at various features that WinJS provides for building Windows Runtime apps using JavaScript, HTML, and CSS. These features include namespaces, modules, promises, and query selectors. These are features used in almost all the applications that you build using WinJS. By taking advantage of the features like namespaces and modules, you can make your app easier to maintain, instead of adding everything under the global namespace.