Javascript For Loops

Javascript Loops

In Java Script Loops are used to execute the same block of code a specified number of times or while a specified condition is true. It means repeating a block of code when a condition is true. 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.The JavaScript for loop is similar to the Java,C and C++ for loop. A for statement looks as follows:

Syntax

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

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>
</body>
</html>

Explanation: The example defines a loop that start 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.

The increment parameter could also be negative, and the less than & equal to (<=) could be any comparing statement.

Output

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

Looping Through an Array

Sometimes you will want to be able to loop through each ele-ment in the array. This can be done using a for loop so that the index variable of
the loop matches one of the array indexes for each iteration through the loop.

Example

<body>
<script>
<!–var myArray = new Array(3);
myArray[0] = “Item 0”;
myArray[1] = “Item 1”;
myArray[2] = “Item 2”;
for (i = 0; i < myArray.length; i++) {
document.write(myArray[i] + “<br>”);
}
// –>
</script>
</body>
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