JavaScript isNaN

JavaScript isNaN function determines whether the value passed as an argument is not a number.

The syntax is therefore the following: isNaN(value).

The function returns a Boolean value that is true if the argument passed is not a number, otherwise it returns false.

JavaScript isNaN – examples

In all the examples presented under the isNaN function gives true:



isNaN('13years');
isNaN('thirteen');
isNaN('13:50');
isNaN('13-01-20');
isNaN('13 01 20');
isNaN('true');

Instead in these other cases it has false value:



isNaN('13.50');
isNaN('13');
isNaN('');

As we can see therefore even if I pass the empty string it gives false as a result, as if it were a number.

Furthermore, even if we pass a number as a string, it always returns false, as in the example below:



var num = '13';
console.log(isNaN(num));

In the browser console we will display false, because the variable num is interpreted as a number.