Learning JavaScript, 3rd Edition

Chapter 4. Control Flow

A common metaphor given to beginning programmers is following a recipe. That metaphor can be useful, but it has an unfortunate weakness: to achieve repeatable results in the kitchen, one has to minimize choices. Once a recipe is refined, the idea is that it is followed, step by step, with little to no variation. Occasionally, of course, there will be choices: “substitute butter for lard,” or “season to taste,” but a recipe is primarily a list of steps to be followed in order.

This chapter is all about change and choice: giving your program the ability to respond to changing conditions and intelligently automate repetitive tasks.

Note

If you already have programming experience, especially in a language with a syntax inherited from C (C++, Java, C#), and are comfortable with control flow statements, you can safely skim or skip the first part of this chapter. If you do, however, you won’t learn anything about the gambling habits of 19th-century sailors.

A Control Flow Primer

Chances are, you’ve been exposed to the concept of a flowchart, which is a visual way of representing control flow. As our running example in this chapter, we’re going to write a simulation. Specifically, we are going to simulate a Midshipman in the Royal Navy in the mid-19th century playing Crown and Anchor, a betting game popular at the time.

The game is simple: there’s a mat with six squares with symbols for “Crown,” “Anchor,” “Heart,” “Club,” “Spade,” and “Diamond.” The sailor places ...