Why is this grouping operator + function immediately invoked

Question

I\'am studying the behaviour of Immediatly Invoked Function Expressions (IIFE) and while doing that I encounterd the following situation.

(function () {
             


        

Answer 1

You can write a IIFE also like that: (function () {})()

By omitting the semicolon, your first codesnippet actually calls the first function with the second IIFE handed over as parameter for the first.

                    executing as parameter for the first IIFE
                                               \/ 
(function () {document.write("bar");})( (function () {document.write("foo");}());)

which first prints foo and then bar unlike:

(function () {
    document.write("bar");
})();

(function () {
    document.write("foo");
}());

which prints barfoo or

(function () {
    document.write("bar");
});

(function () {
    document.write("foo");
}());

where the first now is solely considered as grouping operator.