A Dart web application runs inside the browser (HTML) page that hosts the app; a single-page web app is more and more common. This page may already contain some HTML elements or nodes, such as <div> and <input>, and your Dart code will manipulate and change them, but it can also create new elements. The user interface may even be entirely built up through code. Besides that, Dart is responsible for implementing interactivity with the user (the handling of events, such as button-clicks) and the dynamic behavior of the program, for example, fetching data from a server and showing it on the screen. In previous chapters, we explored some simple examples of these techniques. Compared to JavaScript, Dart has simplified the way in which code interacts with the collection of elements on a web page (called the DOM tree). This chapter teaches you this new method using a number of simple examples, culminating with a Ping Pong game. The following...