NaN

NaN is short for Not a Number. In JavaScript, dividing a number by 0 returns NaN.

Any operation involving NaN always returns NaN.

 
<!DOCTYPE html>
<html>
<head>
    <title>Number Example</title>
    <script type="text/javascript">
          
            document.writeln(NaN /10); 

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

Click to view the demo

NaN is not equal to any value, including NaN.

 
<!DOCTYPE html>
<html>
<head>
    <title>Number Example</title>
    <script type="text/javascript">
            document.writeln(NaN == 0); //false 
            document.writeln(NaN == NaN); //false 

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

Click to view the demo

JavaScript isNaN() function tells if the value is "not a number".

 
<!DOCTYPE html>
<html>
<head>
    <title>Number Example</title>
    <script type="text/javascript">
        document.writeln(isNaN(NaN)); //true 
        document.writeln(isNaN(10)); //false - 10 is a number 


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

Click to view the demo

isNaN tries to convert the value passed to number.

 
<!DOCTYPE html>
<html>
<head>
    <title>Number Example</title>
    <script type="text/javascript">
        document.writeln(isNaN("10")); //false - can be converted to number 10 
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

true is converted to 1 and false is converted to 0.

 
<!DOCTYPE html>
<html>
<head>
    <title>Number Example</title>
    <script type="text/javascript">
        document.writeln(isNaN(true)); //false - can be converted to number 1 
        document.writeln(isNaN(false)); //false - can be converted to number 0 
    </script>
</head>
<body>
</body>
</html>

Click to view the demo