NaN is a JavaScript property, which is "Not-a-Number" value. This shows it is not a legal number.
Syntax
Here’s the syntax −
Number.NaN
Example
To find out whether value is NaN, use the Number.isNaN() or isNan() method. Here’s an example to check −
Live Demo
<!DOCTYPE html> <html> <body> <button onclick="display()">Check</button> <p id="test"></p> <script> function display() { var a = ""; a = a + isNaN(6234) + ": 6234<br>"; a = a + isNaN(-52.1) + ": -52.1<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>