Cannonball and Slingshot

In this chapter, you learned how to create two ballistics applications. It is important to understand how they are the same and how they are different. The programming techniques and HTML5 features include

programmer-defined objects

setInterval to set up a timing event for the animation, as done for the bouncing ball

building an array using the push method and using the array as a list of what to display

modifying arrays using the splice method

the use of trig functions with calculations to rotate the cannon and to resolve the horizontal and vertical velocities so as to simulate gravity

using a form for player input

handling mouse events (mousedown, mousemove, mouseup), with addEventListener to obtain player input

move drawing arcs, rectangles, lines and images on a canvas

The technique of programmer-defined objects and the use of an array of objects to display will come up again in later chapters. The next chapter focuses on a familiar game known as either memory or concentration. It will use a different timing event as well as the Date function, introduced in Chapter 1.