Try this:
var a = 'asdf';
var b = null;
var intA = parseInt(a);
var intB = parseInt(b);
console.log(intA); //logs NaN
console.log(intB); //logs NaN
console.log(intA==intB);// logs false
If intA == intB were true, that might lead you to conclude that a==b, which it clearly isn't.
Another way to look at it is that NaN just gives you information about what something ISN'T, not what it is. For example, if I say 'an apple is not a gorilla' and 'an orange is not a gorilla', would you conclude that 'an apple'=='an orange'?
