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How to use NaN values in JavaScript_Basics

WBOYOriginal: 2016-05-16 15:56:321240browse

The literal constant NaN without quotes is a special value, which means it is not a non-number. Since NaN always compares to any number, including NaN, it is usually an error condition used to indicate a function that should return a valid number.

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

You can access properties using the following syntax:

var val = Number.NaN;

Example:

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

<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.")
  } 
  alert("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>

This will produce the following results:

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

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