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.
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.