Is NaN equal to NaN?

Question

parseFloat(\"NaN\")

returns \"NaN\", but

parseFloat(\"NaN\") == \"NaN\"

returns false. Now, that\'s probably a go

Answer 1

isNaN works for all values that aren't numbers

isNaN('foo') == true
isNaN(NaN) == true
isNaN(12) == false
isNaN([1,2,3]) == true

If, however you want to check for NaN specifically, or avoid type coercion;
you can use Number.isNaN instead

Number.isNaN('foo') == false
Number.isNaN(NaN) == true
Number.isNaN(12) == false
Number.isNaN([1,2,3]) == false

Answer 2

I'm working with Google Apps Script and so I'm stuck with ECMA 5. Similar to Electric Coffee's answer, here's what I was able to figure out that seems to give a sure answer as to whether or not a value is actually NaN, not if a value is NaN but if it is actually NaN itself:

function isThisNaN(x)
{ 
    return isNaN(x) && Object.prototype.toString.call(x) === '[object Number]'; 
}
console.log(isThisNaN(NaN)); // true

lol Just funny to me that Object.prototype.toString.call(NaN) equals '[object Number]'. My newbie brain tells me that NaN is "Not a Number" but sadly it's just not that simple.

EDIT: I guess I should have said how I ended up at this article. I went with the idea that surely a string that doesn't contain a number wouldn't be treated as a number... well, I ended up finding this out:

isNaN('a'); // true
isNaN(' '); // false

so even though ' ' is a non-numerical string it apparently gets coaxed into a number (0).

console.log(Number(' ')); // 0.0

however...

console.log( 0  ? true : false); // false
console.log(' ' ? true : false); // true

After reading more I do understand it a bit better but wow what a mental crapstorm for a newbie lol