The token { at the beginning of a statement might mean the start of an object literal, or it might mean the start of a statement block. JavaScript assumes it's the latter, a statement block.
Thus
{} + ""
is just an empty statement block followed by the expression + "", which will be interpreted as 0 due to the semantics of the unary + operator.
In the other one, {} is not at the beginning of a statement, so it's unambiguously an (empty) object literal.
