JavaScript Number isNAN() Method

The JavaScript Number isNaN() method is used to determine whether a given number is a "NaN" or not. The "NaN" stands for 'Not a Number'. If you are familiar with this acronym, you have an idea about the purpose of this method. The method returns a boolean value 'true', if the given value is not a number, and 'false' otherwise.

isNan() vs Number.isNan()

The isNaN() method returns true; if the value is not a number, whereas the Number.isNaN() returns true; if the number is not a number(NaN).

Note: The isNaN() method converts the value to the number; if neccessary.

Syntax

Following is the syntax of JavaScript Number isNaN() method −

Number.isNaN(value)

Parameters

This method accepts a parameter named 'value'. The same is described below −

value − The value to be checked.

Return value

This method returns 'true'; if the value is not a number (NaN); 'false' otherwise.

Example 1

If the passed value is a number, this method returns 'false'.

In the following example, we are passing the '1234' value as an argument to the isNaN() method to check whether it is a number or not.

<html>
<head>
<title>JavaScript isNAN() Method</title>
</head>
<body>
<script>
   let value = 1234;
   document.write("Given value = ", value);
   document.write("<br>Value is 'NaN' or not? ", Number.isNaN(value));//return false
</script>
</body>
</html>

Output

The above program returns 'false'.

Given value = 1234
Value is 'NaN' or not? false

Example 2

Here's another example of the JavaScript Number isNaN() method. We are passing 'NaN' as an argument to this method to determine whether the value 'NaN' is Not a number. Since it is not a number, it will return true.

<html>
<head>
<title>JavaScript isNAN() Method</title>
</head>
<body>
<script>
   let value = NaN;
   document.write("Given value = ", value);
   document.write("<br>Value is 'NaN' or not? ", Number.isNaN(value));//return true
</script>
</body>
</html>

Output

Once the above program is executed, it will return 'true'.

Given value = NaN
Value is 'NaN' or not? true

Example 3

Let's compare the results of passing the same value to both 'isNaN()' and 'Number.isNaN()' methods.

<html>
<head>
<title>JavaScript isNAN() Method</title>
</head>
<body>
<script>
   let value = 'Hello';
   document.write("Given value = ", value);
   document.write("<br>The 'isNaN()' method returns: ", isNaN(value));//returns true
   document.write("<br>The 'Nunber.isNaN()' method returns: ", Number.isNaN(value));// returns false
</script>
</body>
</html>

Output

The above program produces the following output −

Given value = Hello
The 'isNaN()' method returns: true
The 'Nunber.isNaN()' method returns: false

Example 4

Let's see the real-time usage of this method. We will use the method's result within the conditional statement to print the inner statement based on the result produced by this method.

<html>
<head>
<title>JavaScript isNAN() Method</title>
</head>
<body>
<script>
   function verify(value){
      if(Number.isNaN(value)){
         return true;
      }
      else{
         return false;
      }
   }
   let val1 = NaN;
   let val2 = 122;
   let val3 = 'abc';
   document.write("'", val1, "' is (not a number)  = ", verify(val1));
   document.write("<br>'", val2, "' is (not a number)  = ",  verify(val2))
   document.write("<br>'", val3, "' is (not a number)  = ", verify(val3));
</script>
</body>
</html>

Output

After executing the above program, it displays the following statements −

'NaN' is (not a number) = true
'122' is (not a number) = false
'abc' is (not a number) = false