As Web developers, we tend to get excited by new technologies that enable us to create ever more engaging, interactive Web pages. 3D graphics with WebGL? Absolutely. Advanced audio capabilities with WebAudio? Sure thing. Real-time collaboration applications using the Web camera and microphone? Sign me up! Less exciting, though equally important, are the technologies that allow us to build applications that run more efficiently and provide a better overall user experience. This is where an API like PageVisibility comes in. The Page Visibility API performs a simple but important function – it lets your application know when a page is visible to the user. This basic piece of information enables the creation of Web pages that behave differently when they are not being viewed.