Any difference between f() and (f())?

Question

Any difference between

var myfunc = (function () { return function () { ... } }());

and

var myfunc = function () { return function () { ... } }();

Is it just a matter of style or is there more to the surrounding () in the first form?

Answer 1

Nope. Or at least not in your example.

The outer parens only matter when the function keyword would be the first token in a statement.

// cool
var foo = function(){}();
var foo = (function(){}());

// also cool
(function(){}());

// not cool, syntax error
// parsed as function statement, expects function name which is missing
function(){}();

// also not cool, syntax error
// declares a function, but can't be executed immediately
function foo(){}();

When function is the first token in a statement, it's a function declaration (think named function), which behaves slightly differently than function in all other contexts. That leading paren forces the parses to treat it like a function expression (think anonymous function) instead, which allows immediate execution.

See: What is the difference between a function expression vs declaration in JavaScript?

If you start the line or statement with something else, like variable declaration, it technically doesn't matter at all.

Answer 2

No difference, though Crockford advises the use of the former, to ascertain that it's being treated as a function expression.

For more info, read these:

• Immediately-Invoked Function Expression (IIFE)
• Named function expressions demystified