Question

Bootstrap css uses the following:

!function( $ ) {
}( window.jQuery )

That’s different than the self-invoking anonymous function call that I originally learned:

(function($) {
})(jQuery);

Q: Is that just preference you think? I mean the not symbol instead of enclosing it in parenthesis.

Answer 1

“Q: Is that just preference you think?”

Yes, but using a unary ! operator, you can avoid a few bugs when you forget a semicolon before the IIFE, which can cause the () to be interpreted as a function call.

alert('foo')  // alerts 'foo'

(function() {  // TypeError: undefined is not a function
    alert('bar');
})()

Here the outer () is interpreted as a function call. It’s trying to call whatever was returned from the alert() function, which of course returns undefined, which isn’t a function.

---

alert('foo')  // alerts 'foo'

!function() {
    alert('bar');  // alerts 'bar'
}()

No troubles with this one, since the ! is a unary operator that only evaluates the operand to its right.