Why isn't this returning null?

Question

Let's run this javascript code:

var value = parseInt("");
console.log(value != Number.NaN? value : null);

Why does this code outputs Nan in the console instead of null?

How can I change my code to actually get a null object ?

I try to wrap my code in a function like this:

function parseIntOrDefault(value, def){
    var candidate = parseInt(value);
    if(candidate != Number.NaN) return candidate; else return def;    
}

console.log(parseIntOrDefault('', null));

But this behaves the same.

Here is a jsFiddle that illustrate my issue: http://jsfiddle.net/stevebeauge/BRP94/

Answer 1

You should use

isNaN(value);

to check for NaN

Because:

console.log(NaN === NaN); // false!

NaN is not equal to itself.

This may seem weird but it makes sense if you think about the nature of NaN.

Let's say you have this code:

var a, b, c;
// a = 0;oops a is still undefined so we'll get NaN if we do an operation with it
b = 5;
c = 6
if (a + b === a + c) {
    console.log("math error?");
}

You don't want to come to the seeming conclusion that 5 === 6.

Answer 2

if(isNaN(candidate))return null; else return candidate;