How do you check that a number is NaN in JavaScript?

NaN is a JavaScript property, which is Not-a-Number value. This shows it is not a legal number. Here's the syntax -

Syntax

Number.NaN

To find out whether a number is NaN, use the Number.isNaN() or isNan() method. Here's an example to check -

Example

<!DOCTYPE html>
<html>
  <body>
   <button onclick="display()">Check</button>
   <p id="test"></p>
   <script>
     function display() {
      var a = "";
      a = a + isNaN(434) + ": 434<br>";
      a = a + isNaN(-23.1) + ": -23.1<br>";
      a = a + isNaN('Hello') + ": 'Hello'<br>";
      a = a + isNaN(NaN) + ": NaN<br>";
      a = a + isNaN('') + ": ''<br>";
      a = a + isNaN(0) + ": 0<br>";
      a = a + isNaN(false) + ": false<br>";

      document.getElementById("test").innerHTML = a;
     }
   </script>
  </body>
</html>
Updated on: 2020-06-17T06:30:40+05:30

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