Lesson 10. JavaScript For Loop

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Loops in JavaScript are used to execute the same block of code a specified number of times or while a specified condition is true.

Examples:

<p>Explanation:</p>

<p>This for loop starts with i=0.</p>

<p>As long as <b>i</b> is less than, or equal to 5, the loop will continue to run.</p>

<p><b>i</b> will increase by 1 each time the loop runs.</p>

</body>
</html>

Result:

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5

Explanation:

This for loop starts with i=0.

As long as i is less than, or equal to 5, the loop will continue to run.

i will increase by 1 each time the loop runs.

Looping through HTML headers

</body>
</html>

Result:

This is header 1

This is header 2

This is header 3

This is header 4

This is header 5

This is header 6

JavaScript Loops

Very 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.

Syntax

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

Example

Explanation: 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.

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

<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>
</body>
</html>

Result

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

The while loop

The while loop will be explained in the next chapter.

« Lesson 9. JavaScript Functions	Lesson 11. JavaScript While Loop »
Posted on Wednesday, January 28th, 2009 at 3:50 pm under Javascript For Beginners \| RSS 2.0 Feed

One Response to “Lesson 10. JavaScript For Loop”

Contents: Javascript for Beginners Says:
January 28th, 2009 at 6:20 pm
[...] Lesson -10. JavaScript For Loop [...]

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