JSON left out Infinity and NaN; JSON status in ECMAScript?

Question

Any idea why JSON left out NaN and +/- Infinity? It puts Javascript in the strange situation where objects that would otherwise be serializable, are not, if they contain NaN or +/- infinity values.

Looks like this has been cast in stone: see RFC4627 and ECMA-262 at the top of p. 197:

Finite numbers are stringified as if by String(number). NaN and Infinity regardless of sign are represented as the string null.

Answer 1

Could you adapt the null object pattern, and in your json represent such values as

myNum:{
   isNaN:false,
   isInfinity:true
}

Then when checking, you can check for the type

if (typeof(myObj.myNum) == 'number') {/* do this */}
else if (myObj.isNaN) {/* do that*/}
else if (myObj.isInfinity) {/* Do another thing */}

I know in Java you can override serialization methods in order to implement such a thing. Not sure where your serializing from, so I can't give details on how to implement it in the serialization methods.

Answer 2

Could it be because JSON is intended to be a data interchange format that can be used in a variety of platforms and allowing NaN/Infinity would make it less portable?

Answer 3

Infinity and NaN aren't keywords or anything special, they are just properties on the global object (as is undefined) and as such can be changed. It's for that reason JSON doesn't include them in the spec -- in essence any true JSON string should have the same result in EcmaScript if you do eval(jsonString) or JSON.parse(jsonString).

If it were allowed then someone could inject code akin to

NaN={valueOf:function(){ do evil }};
Infinity={valueOf:function(){ do evil }};

into a forum (or whatever) and then any json usage on that site could be compromised.