JavaScript !function(){} [duplicate]

Question

This question already has answers here:

What does the exclamation mark do before the function? (8 answers)

Closed 8 years ago.

when looking at the minified Sizzle code, I noticed that it begins like this:

!function(a){//...

  }(window)

Why is there an exclamation point at the beginning?

I thought that ! was the not operator.

Thank you.

Edit:

Full Code.

Answer 1

!function(a){/* ... */}();

Using an unary operator to invoke an IIFE is common practice. That's a common shorthand for:

(function(a){/* ... */}());

or:

(function(a){/* ... */})();

You can also substitute the not unary operator with any other unary operator:

-function(a){ /* ... */ }();
+function(a){ /* ... */ }();
/* ... etc. */

Answer 2

gives a good explaination for function invocation https://github.com/airbnb/javascript/issues/44#issuecomment-13063933

!function () {}();

is equivalent to

(function(){})();

except the author is saving 1 byte of code.

In many cases, it's about saving bytes.

!function aaa(){}()
!function bbb(){}();

is the same as this:

!function aaa(){}()
;(function bbb(){})();

notice the ";" in that last bit. That is defensive, as it protects your code a bit from runaway js that might preceed it.

funny, I asked this same question some time ago:

Came across a convention I've never seen. What does it do? !function

great reference on it: What does the exclamation mark do before the function?