Javascript variable / 'NaN' behaving weirdly

Question

I have a couple of textboxes, Which return javascript Number values if valid data is in the textboxes, otherwise NaN. I get this strange behavior.

Answer 1

NaN is not equal to anything, not even NaN.

Reference at MDN

More detailed SO question and answer

For the authoritative source, see the ECMAScript 5 Official Specification, sections 11.9.1 and 11.9.3:

1. If Type(x) is the same as Type(y), then
     [...]
  c. If Type(x) is Number, then
     i. If x is NaN, return false.
    ii. If y is NaN, return false.
        [...]