CODEWITHSUNDEEP
javascriptnaninfinity
igorpavlov
igorpavlov

Reputation: 3626

JavaScript - should Infinity and NaN be numbers?

Few experiments

I am going to write some Maths expressions in JS and wondered:

typeof(Infinity)              // "number", in Maths it is NOT a number
typeof(NaN)                   // "number", how NaN (Not A Number) can actually be a number?

And just a few more experiments:

Infinity === Infinity         // TRUE
Infinity * 2 === Infinity * 5 // TRUE, so 2===5 if Infinity !== 0?

However, this makes sense to me:

NaN * 2 === NaN * 5           // FALSE

Questions

Upvotes: 0

Views: 220

Answers (2)

ap3rus
ap3rus

Reputation: 91

There's an answer about inequality of two NaNs here - Why is NaN === NaN false?. As for the infinities, this is a pure math - infinity times anything is infinity. Lastly, typeof returns "number" for Infinity and NaN just because these are constants of numeric type in JS.

Upvotes: 1

T.J. Crowder
T.J. Crowder

Reputation: 1074218

Why JS is designed so? Was there a particular reason for that?

JavaScript takes both NaN (including the fact that it's never equal to itself) and infinity directly from IEEE-754, the go-to standard for floating point numbers in computing, which is also used by many other languages. (Specifically, it uses a "quiet NaN".) IEEE-754, in turn, gets a lot of this from mathematic theory (e.g., Infinity + 1 === Infinity, apparently this is considered true for some kinds of numbers, but I am not a mathematician; I would assume the designers of the standard had a reason for following that definition).

Are there potentials threats when writing Maths expressions in JS?

I wouldn't call them threats, but: NaN will propagate throughout any calculation where it comes up. Other than that, you have the usual issues with precision discussed in this question and its answers.

Upvotes: 2

Related Questions