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JavaScript Number - NaN

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Description

Unquoted literal constant NaN is a special value representing Not-a-Number. Since NaN always compares unequal to any number, including NaN, it is usually used to indicate an error condition for a function that should return a valid number.

Note − Use the isNaN() global function to see if a value is an NaN value.

Syntax

The syntax to use NaN is −

var val = Number.NaN;

Example

Try the following example to learn how to use NaN.

Live Demo 
<html>
   <head>      
      <script type = "text/javascript">
         <!--
            function showValue() {
               var dayOfMonth = 50;
               
               if (dayOfMonth < 1 || dayOfMonth > 31) {
                  dayOfMonth = Number.NaN
                  alert("Day of Month must be between 1 and 31.")
               }
               Document.write("Value of dayOfMonth : " + dayOfMonth );
            }
         //-->
      </script>      
   </head>
   
   <body>
      <p>Click the following to see the result:</p>      
      <form>
         <input type = "button" value = "Click Me" onclick = "showValue();" />
      </form>      
   </body>
</html>

Output

javascript_number_object.htm
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