Question

JavaScript’s quirky weakly-typed == operator can easily be shown to be non-transitive as follows:

var a = "16";
var b = 16;
var c = "0x10";
alert(a == b && b == c && a != c); // alerts true

I wonder if there are any similar tricks one can play with roundoff error, Infinity, or NaN that could should show === to be non-transitive, or if it can be proved to indeed be transitive.

Answer 1

The === operator in Javascript seems to be as transitive as it can get.

NaN is reliably different from NaN:

>>> 0/0 === 0/0
false
>>> 0/0 !== 0/0
true

Infinity is reliably equal to Infinity:

>>> 1/0 === 1/0
true
>>> 1/0 !== 1/0
false

Objects (hashes) are always different:

>>> var a = {}, b = {};
>>> a === b
false
>>> a !== b
true

And since the === operator does not perform any type coercion, no value conversion can occur, so the equality / inequality semantics of primitive types will remain consistent (i.e. won’t contradict one another), interpreter bugs notwithstanding.