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Javascript Number - NaN

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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.


You can access this property using the following syntax:

var val = Number.NaN;


Here dayOfMonth is assigned NaN if it is greater than 31, and a message is displayed indicating the valid range:

<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.")
   alert("Value of dayOfMonth : " + dayOfMonth );
<p>Click the following to see the result:</p>
<input type="button" value="Click Me" onclick="showValue();" />

This will produce following result:

Day of Month must be between 1 and 31. Value of dayOfMonth : NaN

To understand it in better way you can Try it yourself.

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