Comparing NaN values for equality in Javascript

Question

I need to compare two numeric values for equality in Javascript. The values may be NaN as well. I\'ve come up with this code:

if (val1 == val2 |         


        

Answer 1

Equality comparison with NaN always results in False.

We can go for the javascript function isNaN() for checking equality with NaN. Example:

1. isNaN(123) //false

2. var array = [3, NaN];

for(var i = 0 ; i< array.length; i++){
  if(isNaN(array[i])){
      console.log("True ---- Values of " + i);
    } else {
      console.log("false ---- Values of " + i);
    }
}

Results:

false ---- Values of 0

True ---- Values of 1

Answer 2

For Numeric cases the solution is fine but to extend it to work for other data-types as well my suggestion would be as follows:

if(val1 === val2 || (val1 !== val1 && val2 !== val2))

Reason being global isNaN is erroneous. It will give you wrong results in scenarios like

isNaN(undefined); // true
isNaN({});        // true
isNaN("lorem ipsum"); // true 

I have posted a comprehensive answer here which covers the NaN comparison for equality as well.

How to test if a JavaScript variable is NaN

Answer 3

if(val1 == val2 || (isNaN(val1) && isNaN(val2)))

Nothing to improve. Just add the parentheses to make it clear to everyone.

Answer 4

And what's about the function Number.isNaN() ? I believe this must be used whenever is possible.

> NaN === NaN
false
> Number.isNaN
ƒ isNaN() { [native code] }
> Number.isNaN() === Number.isNaN()
true

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN

Answer 5

if ( val1 === val2 )

If either one or both are NaN it will evaluate to false.

Also, NaN !== NaN

Answer 6

I created this answer after reviewing the suggestions of ThiefMaster, Esailija, Joachim Isaksson and davidchambers. Can this be further improved?

// Determines if two numeric values are equal.
// Also returns true when both parameters are NaN.
function areEqualNumeric(val1, val2) {
    return val1 === val2 || (val1 !== val1 && val2 !== val2);
}