(function a() {
    return "b";
}());

function a() {
   return b;
}();

Uncaught SyntaxError: Unexpected token )

var c = function a() {
   return b;
}();
console.log(c); // prints b

function a() {
    return "b";
}()

function a() {
    return "b";
}

() // not allowed - empty expression

() // meaningless
2 + 3 * 4 // 5
(2 + 3) * 4 // 20