JavaScript While Loop

JavaScript While Loop check condition and execute while block for a specify number of times, until while condition become false.

In while loop condition check first. If condition become true, execute a block of code executed.

Syntax

while (condition) {
    statements;     // Do stuff if while true
    increment;      // Update condition variable value
}

while (true) {     // condition evaluates to true
    ...
    ...
}

while (1) {            // Condition always true
    ...
    ...
}

Example: Following while loop example execute block of code until number value become 10. When number value become 11 the condition no longer satisfy and finally skip to execute while block.

<script>
    number = 1;
    while (number <= 10) {
        document.writeln(number + " times");
        number++;
    }
    document.writeln("Total " + (number - 1) + " times loop repeat");
</script>

Example Result

Array Loops in JavaScript

While loop to go through array,

JavaScript array.length property indicates length of a array.

<script>
    var arr = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100];
    number = 0;
    while (number < arr.length) {
        document.writeln("Value of arr[" + number + "] : " + arr[number]);
        number++;
    }
    document.writeln("End of Loop.");
</script>

Example Result

Reverse Array Loop in JavaScript

Following example display all array elements value in reverse order.

<script>
    var arr = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100];
    number = arr.length;
    while (number--) {
        document.writeln("Value of arr[" + number + "] : " + arr[number]);
    }
    document.writeln("End of Loop.");
</script>

Example Result