The for Loop

The for loop is made of two separate parts - the condition and the statement, as shown below in the syntax example.

for (initialValue ; condition ; adjustInitialValue)
   {
   statement
   } 

The condition of the for loop is the three values (initialValue, condition, and adjustInitialValue) within the opening and closing brackets after the for keyword. The statement is the statement given within the curly braces. The statement is executed on the variable declared for initialValue and then on adjustInitialValue. The loop iterates through itself until the condition is satisfied, no matter how long it takes. Care should be taken to not create an infinite loop that has a condition that won't ever be satisfied by the rest of your script.

The initialValue is a variable that defines the initial starting value for the loop. This variable can be defined within the loop or by a separate variable declaration not within the loop. Take care that the variable is of the Global type of variable - JavaScript does not allow the use of a Local type of variable outside of the function it was created in. The condition is the section in which you'll use the operators learned in a previous discussion. It is used to provide the amount of times to iterate through the loop. The third section of the loop is adjustInitialValue, which is used to make an adjustment to the initialValue section. This adjustment may be any increment, decrement, or any other operation you may have a use for. Obviously, the adjustment would reflect the type of data you are using and the outcome you were looking for.

The below example shows the use of a loop very well. It is used to print the multiplication table of 5, up to 5 X 12. for

(var varOne = 0 ; varOne <= 12 ; varOne++)
   {
   document.write("5 X " + varOne + "=" + 5*varOne + "<br>");
   } 

The example shows the for keyword followed by the initial value within the newly created variable, varOne. The value of varOne is initially zero. The next part of the statement tells you that the maximum amount of times the loop is to iterate is 12 times, as indicated by the "varOne <= 12" statement. Next comes the statement that changes the initial value of zero within varOne. In this case the change is a simple post-decrement operator that increases the value of varOne by One. After each iteration, the document.write statement is printed to the screen. The document.write statement does the multiplication used to display the multiplication by five results, not the loop condition. The output looks as follows.

5 X 0=0
5 X 1=5
5 X 2=10
5 X 3=15
5 X 4=20
5 X 5=25
5 X 6=30
5 X 7=35
5 X 8=40
5 X 9=45
5 X 10=50
5 X 11=55
5 X 12=60

You can see now how simple it is to create a for loop. This is most likely the reason why it is used so often.

Loops
JavaScript Introduction
The while Loop

The JavaScript Chronicles