Key to building the interactive and responsive UI is event handling. The greater the number of events available, the better the interaction between the user and the application. For example, if we are dragging an element on the screen and if the underlying platform happens to only raise two events—one at the beginning of the drag and one at the end of the drag—then we only get two chances to interact with the element and use the corresponding handlers to respond to those events. However, imagine if the platform also raises the event while the element is on the move. In this way, we can also show the trajectory to the user to show how the element is moving from the starting point to the end point.

So far in different chapters, we have looked at different events raised by the components and we handled some of them. When a web application is used on the touch device, it typically interprets the mouse events to provide the required interactivity. This may put limitations on the user...