Why does “a + + b” work, but “a++b” doesn't?

Question

I was fiddling around with different things, like this

var a = 1, b = 2;
alert(a + - + - + - + - + - + - + - + b); //alerts -1

and I could

Answer 1

The answer is that ++ is an operator as well as +, and that + + is two + operators, not a ++ operator.

Although it's not Javascript, C++ has similar fun with + and ++ operators. This was investigated in one of the Gurus of the Week from way back when.