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 Javascript parser is greedy (it matches the longest valid operator each time), so it gets the ++ operator from a++b, making:

(a++) b

which is invalid. When you put in spaces a + + b, the parser interprets it like this:

(a) + (+b)

which is valid and works out to be three.

See this Wikipedia article on Maximal munch for more details.