Chapter 2. Making Decisions with Conditions

In This Chapter

  • Generating random numbers and integers

  • Working with conditions

  • Using the if-else and switch structures

  • Handling unusual conditions

One of the most important aspects of computers is their apparent ability to make decisions. Computers can change their behavior based on circumstances. In this chapter, you discover how to maximize this decision-making ability.

Working with Random Numbers

Random numbers are a big part of computing. They add uncertainty to games, but they're also used for serious applications, such as simulations, security, and logic. Most languages have a feature for creating random numbers, and JavaScript is no exception. The Math.random() function returns a random floating point value between zero and one.


Technically, computers can't create truly random numbers. Instead, they use a complex formula that starts with one value and creates a second semi-predictable value. In JavaScript, the first value (called the random seed) is taken from the system clock in milliseconds, so the results of a random number call seem truly random.

Creating an integer within a range

Creating a random floating point number between zero and one is easy, thanks to the Math.random() function. What if you want an integer within a specific range? For example, say that you want to simulate rolling a six-sided die. How do you get from the 0-to-1 floating point value to a 1-to-6 integer?

Here's the standard approach:

  1. Get a random float between ...

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