I had to write a routine that increments the value of a variable by 1 if it is a number, or assigns 0 to the variable if it is not a number. The variable can be incremented by the expression, or be assigned null. No other write access to the variable is allowed. So, the variable can be in three states: it is 0, a positive integer, or null.

My first implementation was: v >= 0 ? v += 1 : v = 0

(Yes, I admit that v === null ? v = 0 : v += 1 is the exact solution, but I wanted to be concise then.)

It failed since null >= 0 is true. I was confused, since if a value is not a number, an numeric expression involving it must be false always. Then I found that null is like 0, since null + 1 == 1, 1 / null == Infinity, Math.pow(2.718281828, null) == 1, ...

Strangely enough, however, null == 0 is evaluated to false. I guess null is the only value that makes the following expression false: (v == 0) === (v >= 0 && v <= 0)

So why null is so special in JavaScript?