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JavaScript Number method: isNaN()

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The isNaN() method (of the JavaScript Number object) returns true if value is of type Number and is an integer (within range understood as integers by the browser), otherwise returns false.

 

It has the following syntax with the following parameters:

 

Number.isNaN(x)

 

Parameter

Required / Optional

Description

x

Required

Input parameter

 

The Number.isNaN method is subtly different to the global isNaN function. The latter coerces a value to a number before testing it, whilst the former does not. So, Number.isNaN("NaN") returns false, whilst isNaN("NaN") returns true.

 

EXAMPLE:


HTML USED IN THIS EXAMPLE:
<!DOCTYPE html>
<html> <!-- Copyright (c) Nematrian Limited 2018 -->
<head>
<style>
table,th,tr,td {border: 1px solid black; border-collapse: collapse;}
</style>
</head>
<body>
<table>
<tr>
<th>Example</th>
<th>Resulting value of <code>x</code></th>
</tr>
<tr>
<td><code id="Example"></code></td>
<td><code id="Result"></code></td>
</tr>
</table>

<script>
document.getElementById("Example").innerHTML =
  'var x = Number.isNaN(0/0);';
document.getElementById("Result").innerHTML
  = Number.isNaN(0/0);
</script>

</body>
</html>

FUNCTION THAT MAY ASSIST IN TESTING WHETHER FEATURE IS SUPPORTED:
function isSupportedJavaScriptMethodNumberIsNaN() {
  var z = 12.5; return !!z.isNaN;
}


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