How Number.Nan works in this function?

Question

I think the first condition should be true, Because the argument for parameter x is Number.Nan. And it surely equals with the other Namber.Nan within the first conditional if. But I'm wrong apparently. Why? What is the value of x when it is comparing to Number.NaN?

function clean(x) {
  if (x === Number.NaN) {
    // can never be true
    return null;
  }
  if (isNaN(x)) {
    return 0;
  }
}

console.log(clean(Number.NaN));
// expected output: 0