Decisions and Loops - Beginning JavaScript - page 77

in the initialization part that you initialize variables. In the example, you have declared loopCounter
and set it to the value of 1 . This part is only executed once during the execution of the loops, unlike
the other parts. You don't need to declare the variable if it was declared earlier in the code:

var loopCounter;
for (loopCounter = 1; loopCounter <= 3; loopCounter++)

Initialize loop variable Loop test condition Increment loop variable

for ( loopCounter = 1; loopCounter <= 3; loopCounter++)
{

// execute this code

}

Code looped through

figure 3-10

Following the semicolon, you have the test condition part of the for statement. The code inside
the for statement will keep executing for as long as this test condition evaluates to true . After the
code is looped through each time, this condition is tested. In Figure 3-10, you execute for as long as
loopCounter is less than or equal to 3 . The number of times a loop is performed is often called the
number of iterations .

Finally, you have the increment part of the for loop, where variables in your loop's test condition have
their values incremented. Here you can see that loopCounter is incremented by one by means of the
++ operator you saw in Chapter 2. Again, this part of the for statement is repeated with every loop of
the code. Although we call it the increment part, it can actually be used to decrease, or decrement , the
value—for example, if you wanted to count down from the top element in an array to the first.

After the for statement comes the block of code that will be executed repeatedly, as long as the
test condition is true . This block of code is contained within curly braces. If the condition is never
true , even at the first test of the loop condition, the code inside the for loop will be skipped over
and never executed.

Putting all this together, how does the for loop work?
1.

Execute initialization part of the for statement.

2. Check the test condition. If true , continue; if not, exit the for statement.

3.

Execute code in the block after the for statement.

4. Execute the increment part of the for statement.

5.

Repeat steps 2 through 4 until the test condition is false .