Increment/Decrement Operators

The increment operator is ++. The decrement operator is --. The increment and decrement operators have two versions: prefix and postfix.

The prefix operators are placed before the variable. The postfix operators are placed after the variable. The increment operator adds 1 to a numeric value and decrement operatos subtracts 1 from a numeric value:

 
<!DOCTYPE html>
<html>
<head>
    <title>Operator Example</title>
    <script type="text/javascript">

        var num = 4; 
        document.writeln(num); //4 
        ++num; 
        document.writeln(num); //5 
        --num; 
        document.writeln(num); //4
        
    </script>

</head>
<body>
  
</body>
</html>

Click to view the demo

The difference between postfix and prefix: the increment or decrement doesn't occur until the containing statement has been evaluated.