javascript - Why is this grouping operator + function immediately invoked -

javascript - Why is this grouping operator + function immediately invoked -

i'am studying behaviour of immediatly invoked function expressions (iife) , while doing encounterd next situation.

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

i thought first grouping operator function look within without calling it. sec grouping operator function look phone call of function.

what find unusual both invoked, why that?

(function () { document.write("bar"); }) var x = 1; (function () { document.write("foo"); }());

when break 2 inserting variable declaration in between, it's writes foo. expected.

because forgot semicolon after first function expression:

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

otherwise sec "grouping operator" interpreted function call. this:

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

is same as:

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

reordering makes bit easier see. remember white space characters have no meaning in javascript , ignored.

javascript iife