Javscript Loops Tutorials - For Loop and While Loops

Full Tutorial List           Tutorials (50)       Sept 01, 2009

JavaScript For Loops?


In JavaScript for loop are used when you know in advance how many times the script or a piece of code should be executed. Loops help to remove situations where you have to enter the same piece of code multiple times. Loops will execute a specified number of times or while a specified condition is true.

Sample Pseudo Code:

for (var=startvalue;var<=endvalue;var=var+increment) 
{
    code to be executed
}

The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10, i will increase by 1 each time the loop runs. 


Example:

<html>
<body>
<script type="text/javascript">
var i=0
for (i=0;i<=10;i++)
{
document.write("The number is " + i)
document.write("<br />")
}
</script>
</table>
</body>
</html>

The output above would be

The number is 0

The number is 1

The number is 2

Etc etc etc


The number is 9 – nine is the last number to be oututed because I has to be less than 10.

While Loop

The JavaScript while loop is much simpler than the for loop. It consists of a condition and the statement block.

Pseudo Code:


while (condition)
   {
   ...statements...
   }

As long as the condition evaluates to 'true', the program execution will continues to loop through the statements.

Example


<html>
<body>
<script type="text/javascript">
var x = 1;
while (x <= 10)
   {
   document.write("The number is " + x)
   x++;
   }
</script>
</table>
</body>
</html>

The output here is the same as for the FOR loop with 9 being the last number outputted.

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