I have a variable x and I want to test if x is set to NaN. How do I do that?
My first instinct is probably to, you know, test it, like this:
if (x === NaN) { ...
Silly rabbit, no, that would be far too easy. NaN is like NULL in SQL, it is not equal to anything, even itself.
But look, there is a function called isNaN() -- maybe that will do it!
No, so far as I can tell, isNaN() is utterly worthless.
For example, isNaN([""]) properly returns false, but isNaN(["."]) returns true. You don't want do know how I learned about this flaw.
How do I do this?
Turns out, my question is a duplicate of this one, but the selected answer is wrong. The right answer has 20% as many upvotes.
The question has the answer if you read closely enough. That is the way I found it: I was typing out the question and... bingo.
You remember when I wrote "NaN is like NULL in SQL, it is not equal to anything, even itself"? So far as I know, NaN is the only value in Javascript with this property. Therefore you can write:
var reallyIsNaN = function(x) {
return x !== x;
};