!function(){ }() vs (function(){ })()

While reviewing some of the code written in the Twitter Bootstrap Javascript, it looks like they're calling immediately invoked anonymous functions like this:

!function( $ ) {


}(window.jQuery || window.ender);

Where I've traditionally seen this same thing accomplished this way:

(function($) {


})(window.jQuery || window.ender);

The first way seems a bit hacky, and I'm not sure if there is any benefit or reason for doing it this way rather than the second way? Note that I understand how it works, I'm looking to understand why they chose that way to do it.


  • One less character when minified.
  • The ! should handle where other JavaScript code is concatenated before this and doesn't have a trailing semi-colon.

There is not a huge difference. I would use whatever you were more comfortable with. You should probably toss something at the start of your example to avoid...


var lol = function() {


(function() {
    // Irrelevant.


Toss in a leading ; and she works...


...or a ! like the Twitter Bootstrap...



They're both ways of getting past the ambiguity in the grammar. Neither is more "hacky" than the other. It's just a style choice.

You could also do this:

0 + function( $ ) {
  // ...
} ( window.jQuery || window.ender );


parseInt(function( $ ) {
  // ...
} ( window.jQuery || window.ender ) );

Instead of the evaluation step of !undefined you could also use the void operator to remove the ambiguity:

void function($) {
}(window.jQuery || window.ender);

Has a kind of C quality to it ;-)


One answer that I've yet not seen is that it avoids surrounding your entire function with parentheses. Outside of aesthetic considerations, this can be a plus for some editors which use parentheses to determine the level of indentation of a line.


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