Google script parseInt and NaN - how it really works?

Question

I'm going to check if certain variable is a string or number. I use parseInt() function which returns NaN (Not a Number) if value is a string. But, when I try to check it in if statement it looks like "NaN" output can't be treated as a valid condition to check. Any guess why?

function tsCalculate() {
  var string = "Monday";
  var number = 1;
  Logger.log(string);
  Logger.log(number);
  Logger.log("String after parseInt: " + parseInt(string, 10));
  Logger.log("Number after parseInt: " + parseInt(number, 10));
  if ("NaN" == parseInt(string, 10))
  {
    Logger.log("doesn't work");
  }
}

Answer 1

NaN is:

• not a string (it is a value in its own right)
• not equal to other things which are also NaN

Use isNaN to determine if a value is equal to NaN.

if (isNaN(parseInt(string, 10))) {

}

Answer 2

This is just a follow up as I am learning things here. Is NaN a reserved object type? Would the following also be a valid statement:

if (NaN === parseInt(String,10)) {...}