The "for" loop

The "for" loop is a JavaScript "method" that allows a certain action (ie: block of code) to be performed continuously in a variably controlled fashion. It is very similar to a "while" loop in which lines of JavaScript codes can be grouped together and repeated until a certain condition. A real life example of a for loop would be as follows:

for length equal to 0 to length equal to 100

Lets see the general syntax of for loops in JavaScript, where y is an arbitrary variable:

for (var y=0; y<=99; y++){

The above example will alert "hi!" 100 times. Lets look more closely at the heart of a "for" loop:

for (var y=0; y<=99; y++)

It consists of three components:

var y=0 //The starting point of a for loop
y<=99 //The ending boundary of a for loop
y++ //How the "for" loop is incremented. y++ means increment it by one step each time until the boundary.

The part that may be confusing is the last part, "y++". Let's see the same above example, only this time, altering that particular part:

for (var y=0; y<=99; y=y+2){

How many "hi" will be alerted? Well, 50 will, because we are incrementing the "counter" not by 1, but by 2 this time. The point is, you can determine however you want to increment the for loop by assigning a different statement in the third component of the for loop.

Lets see a practical example of a "for" loop than, where it is used to calculate the sum of 1+2+3+.....all the way up to the specified number:

Here's the function that performs this calculation:

<script type="text/javascript">
function cal(){
	var y=1
	var temp=prompt("Please input a positive integer:")
	for (var x=2;x<=temp;x++){

The "for" loop is a major part of any programming language, and JavaScript is no exception. For loops are commonly used with arrays to loop through and process each array element effortlessly.

Follow Us
Facebook Fan Page