Why the answer is False ?

Question

var x= NaN;
var y= x;
if(y===x){
console.log(True);
else console.log(False);

Answer 1

In terms of accepting NaN == NaN, something which is not a number is not necessarily equivalent to something else which also isn't a number.
NaN is non-deterministic value, it has no literal value. So it's comparison of not something == not something is also not something.
https://www.sololearn.com/discuss/1772843/?ref=app
https://www.sololearn.com/discuss/1940153/?ref=app
https://www.sololearn.com/discuss/1747008/?ref=app
https://www.sololearn.com/discuss/1684244/?ref=app
https://www.sololearn.com/discuss/1201484/?ref=app

Answer 2

Seems it's a historical mistake that is difficult to change.
https://stackoverflow.com/questions/10034149/why-is-nan-not-equal-to-nan/10059796#10059796