Tutorial Gateway

JavaScript While Loop

by

The JavaScript While Loop is used to repeat a block of statements for given number of times, until the given condition is False.

The While loop in JavaScript start with the condition, if the condition is True then statements inside the while loop will be executed. If it is false then it won’t be executed at least once. It means, JavaScript while loop may execute zero or more time and the syntax of while loop is:

JavaScript While Loop Syntax

The syntax of the While loop in JavaScript is as follows:

While( Condition )
 {
   statement 1;
   statement 2;
    ………….
 }
This is the statement Outside the While Loop

First compiler check the condition inside the While loop. If the Condition is True then the statement or group of statements under the while loop block will be executed. If it is False, compiler will come out of the while loop and execute other statements outside the while loop.

TIP: For single statement curly braces are not required. However, if we omit them for multiple statements then it will execute the first statement only. It is always good practice to use braces all the time.

JavaScript While Loop Flow Chart

The flow chart of While loop in Javascript is as shown below:

JavaScript While Loop Flow Chart

The JavaScript While loop will check for the condition at the beginning of the loop.

  1. If the While condition is True then it will execute the code inside the while loop.
  2. Next we have to use Increment and Decrement Operator inside the while loop to increment and decrements the value. Please refer Increment and Decrement Operators in JavaScript article to understand the functionality
  3. Again it will check the while condition after the value incremented. As long as the condition is True, the code inside the while loop will be executed.
  4. If it is False then it will exit from the While loop

Let us see the JavaScript While loop example for better understanding

JavaScript While Loop Example

In this program, we declared a number variable and assigned value 6. Using this value, compiler will add those values up to 10.

JAVASCRIPT CODE

<!DOCTYPE html>
<html>
<head>
    <title> JavaScript While Loop </title>
</head>

<body>
    <h1> JavaScript While Loop </h1>
<script>
    var number = 6, total=0;
    while (number <= 10)
    {
        total = total + number;
        number++;
    }
    document.write("Value of Total From the While Loop is = ", total);  
</script>
</body>
</html>

ANALYSIS

  1. In this JavaScript while Loop example, First, the value inside the number variable (6) is tested against the while condition.
  2. If the condition results true then number is added to the total, otherwise it will exit from the loop
  3. In the next line we used ++ operator to increment the number value. After incrementing the process will be repeated until the condition results False.

OUTPUT: Here, Our number = 6. It means, total = 6+7+8+9+10 = 40

JavaScript While Loop 1

Infinite JavaScript While Loop

If you forgot to increment or decrement the value inside the while loop then while loop in JavaScript will execute infinite times (also called as infinite loop). For example:

<!DOCTYPE html>
<html>
<head>
    <title> JavaScript While Loop </title>
</head>

<body>
    <h1> JavaScript While Loop </h1>
<script>
    var x = 1;
    while (x < 10)
    {
        document.write("<br\> Value From the While Loop is = " + x);
    }
</script>
</body>
</html>

OUTPUT:
JavaScript While Loop 2

Here x is always 1 and x is always less than 10. So, JavaScript while loop statement will go on execute infinite times. Now, let us add increment operator (x++) inside the while loop to the above example.

<!DOCTYPE html>
<html>
<head>
    <title> JavaScript While Loop </title>
</head>

<body>
    <h1> JavaScript While Loop </h1>
<script>
    var x = 1;
    while (x < 10)
    {
        document.write("<br\> Value From the While Loop is = " + x);
        x++;
    }
</script>
</body>
</html>

Now, when it reaches 10 the condition will fail. Let us see the output

OUTPUT
JavaScript While Loop 3

Thank You for Visiting Our Blog