Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 2 ■ Data and Decisions
Repeating Things: Loops
In this section, we look at how you can repeat a block of code for as long as a set condition is true. For example, you
might want to loop through each input element on an HTML form or through each item in an array.
Repeating a Set Number of Times: The for Loop
The for loop is designed to loop through a code block a number of times and looks like this:
for( initial-condition; loop-condition; alter-condition ) {
//
// Code to be repeatedly executed
//
}
// After loop completes, execution of code continues here
Like the conditional statement, the for keyword is followed by parentheses. This time, the parentheses contain
three parts separated by a semicolon.
The first part initializes a variable that will serve as the counter to keep track of the number of loops made. The
second part tests for a condition. The loop will keep running as long as this condition is true. The last part either
increments or decrements the counter, created in the first part, after each loop. (The fact that it is after is an important
one in programming as you shall see.)
For example, take a look at a loop that keeps running for as long as loopCounter is less than 10:
for( loopCounter = 1; loopCounter