Sams Teach Yourself JavaScript in 24 Hours

Hour 7. Controlling Flow with Conditions and Loops

What You'll Learn in This Hour: Testing variables with the if statement Using various operators to compare values Using logical operators to combine conditions Using alternative conditions with else Creating expressions with conditional operators Testing for multiple conditions Performing repeated statements with the for loop Using while for a different type of loop Using do...while loops Creating infinite loops (and why you shouldn't) Escaping from loops and continuing loops Looping through an array's properties

Statements in a JavaScript program generally execute in the order in which they appear, one after the other. Because this isn't always practical, most programming languages provide flow control statements that let you control the order in which code is executed. Functions, which you learned about in the previous hour, are one type of flow controlalthough a function might be defined first thing in your code, its statements can be executed anywhere in the script.

In this hour, you'll look at two other types of flow control in JavaScript: conditions, which allow a choice of different options depending on a value, and loops, which allow repetitive statements.