Is isNaN() really necessary?

Question

According to the MDN page¹ regarding isNaN (emphasis mine):

Unlike all other possible values in JavaScript, it is not possible to rely on the equality operators (== and ===) to determine whether a value is NaN or not, because both NaN == NaN and NaN === NaN evaluate to false. Hence, the necessity of an isNaN function.

However, since NaN is the only value in JavaScript that will compare unequal to itself, it is in fact possible to rely on the strict equality operator to determine, unequivocally, wheter a value is NaN or not:

const value = NaN;
console.log(value === value)

That said, what's the explanation for that MDN sentence?

^{PS: I do understand that MDN is not an official documentation (that would be ECMA) and that much like a wiki anyone can edit it. Even so, it's a very reliable source.}

^{1: That paragraph has been edited after this question was posted, as mentioned by the answerer.}

user_9515207 · Answer

No, having a built-in isNaN function isn't necessary. isNaN is just for convenience's sake. Sure, one could manually do:

const isNaN = arg => arg !== arg

for every script you wanted to perform such an operation in, but it'd be tedious.

Or, without the function, consider reading code like:

if (parsedNumber !== parsedNumber) {
  // It's NaN
}

That'd look really weird, and it's in programmers' best interests to have code be as readable as possible.

Is isNaN() really necessary?

1 Answers