JavaScript For Loop

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Loops execute a block of code a specified number of times, or while a specified condition is true.

JavaScript Loops

Often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal lines in a script we can use loops to perform a task like this.

In JavaScript, there are two different kind of loops:

  • for - loops through a block of code a specified number of times
  • while - loops through a block of code while a specified condition is true

The for Loop

The for loop is used when you know in advance how many times the script should run.


for (variable=startvalue;variable<=endvalue;variable=variable+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 5. i will increase by 1 each time the loop runs.

Note: The increment parameter could also be negative, and the <= could be any comparing statement.


<script type="text/javascript">
var i=0;
for (i=0;i<=5;i++)
document.write("The number is " + i);
document.write("<br />");
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The while loop

The while loop will be explained in the next chapter.

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