strange anonymous javascript function call [duplicate]

Question

I was looking at this very cool snippet and i came across this weird line in the js and deleting that prevent the function from being invoked

!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!
function(d, w){
   ...
}(document, window);

,i wrapped the function with ( ) as it supposed to be and it works as intended.

(function(d, w){
    ...
})(document, window);

so my question is what is that weird line and why does it work? my wild guest is that it is some kind IIFE...

Answer 1

And you are right, it is an Immediately-Invoked Function Expression (IIFE)

You can rewrite

!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!+-+-+!
function(d, w){
   ...
}(document, window);

to

!function() {
    ...
}()

and it still works. This is because ! is a unary operator (just like +, -, and ~ -- see https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Expressions_and_Operators). After an unary operator an expression is expected (and evaluated!). The expression can be a function call.

However

!function() {
    ...
}()

is just another expression, so you can put another unary operator in front of it:

+!function() {
    ...
}()

You can continue this pattern as you wish.

Note: Invoking an anonymous function this way, ignores the return value of the function. So only use this, if you are not interested in the return value.

Edit: Added an excellent reference to http://benalman.com/news/2010/11/immediately-invoked-function-expression/ which Daff mentioned in his answer.

Answer 2

The trick is actually the single ! operator there (the entire first line actually does the same thing). This will work just as well:

!function(d, w){
   ...
}(document, window);

As always I can recommend Ben Almans great article on Immediately-Invoked Function Expressions